Biodegradable films and sheets suitable for use as coatings, wraps and packaging materials

ABSTRACT

Biodegradable polymer blends suitable for laminate coatings, wraps and other packaging materials are manufactured from at least one “hard” biopolymer and at least one “soft” biopolymer. “Hard” biopolymers tend to be more brittle and rigid and typically have a glass transition temperature greater than about 10° C. “Soft” biopolymers tend to be more flexible and pliable and typically have a glass transition temperature less than about 0° C. While hard and soft polymers each possess certain intrinsic benefits, certain blends of hard and soft polymers have been discovered which possess synergistic properties superior to those of either hard or soft polymers by themselves. Biodegradable polymers include polyesters, polyesteramides, polyesterurethanes, thermoplastic starch, and other natural polymers. The polymer blends may optionally include an inorganic filler. Films and sheets made from the polymer blends may be textured so as to increase the bulk hand feel. Wraps will typically be manufactured to have good “dead-fold” properties so as to remain in a wrapped position and not spring back to an “unwrapped” form.

BACKGROUND OF THE INVENTION

1. The Field of the Invention

The present invention relates generally to biodegradable polymer blendsand articles manufactured therefrom. More particularly, the presentinvention relates to blends of two or more biopolymers and/or blends ofbiopolymers and fillers that yield sheets and films having improvedphysical properties, such as flexibility, elongation and/or dead-fold.The biodegradable polymer blends may be suitable for a number ofapplications, such as in the manufacture of disposable wraps, bags andother packaging materials or as coating materials.

2. The Relevant Technology

As affluence grows, so does the ability to purchase and accumulate morethings. Never before in the history of the world has their been such alarge number of people with such tremendous buying power. The ability topurchase relatively inexpensive goods, such as books, tools, toys andfood, is a luxury enjoyed by virtually all levels of society, even thoseconsidered to be at the poorer end of the spectrum. Because a largepercentage of what is purchased must be prepackaged, there has been atremendous increase in the amount of disposable packaging materials thatare routinely discarded into the environment as solid waste. Thus, associety becomes more affluent, it generates more trash.

Some packaging materials are only intended for a single use, such asboxes, cartons, pouches, bags and wraps used to package items purchasedfrom wholesale and retail outlets. Even the advent of computers and“paperless” transactions has not stemmed the rising tide of packagingwastes. Indeed, the onset of “e-commerce” has spawned a great mail-orderfad, thus creating a whole new market of individually packaged andshipped items.

Moreover, the modern, fast-paced lifestyle has greatly disruptedtraditional eating routines in which people prepared their own meals andsat down as a family or group. Instead, people grab food on the run,thus creating ever-increasing amounts of fast food packaging materialsthat are used once and then discarded. In view of the high volume ofdisposable packaging materials being generated, some countries,particularly those in Europe, have begun to mandate either the recyclingof fast food generated wastes or the use of packaging materials whichare “biodegradable” or “compostable”. Environmental activists commonlypressure companies that generate solid waste. As a result, large fastfood chains such as McDonald's have been essentially forced todiscontinue the use of certain nonbiodegradable packaging materials suchas foamed polystyrene, either by government fiat or by pressure byenvironmental groups. McDonald's currently uses a combination of paperwraps and cardboard boxes as an interim solution until moreenvironmentally friendly packaging materials can be made on a commercialbasis. There is therefore an ever-present need to develop biodegradablealternatives to nonbiodegradable paper, plastics and metals.

In response to the demand for more environmentally friendly packagingmaterials, a number of new biopolymers have been developed that havebeen shown to biodegrade when discarded into the environment. Some ofthe larger players in the biodegradable plastics market include suchwell-known chemical companies as DuPont, BASF, Cargill-Dow Polymers,Union Carbide, Bayer, Monsanto, Mitsui and Eastman Chemical. Each ofthese companies has developed one or more classes or types ofbiopolymers. For example, both BASF and Eastman Chemical have developedbiopolymers known as “aliphatic-aromatic” copolymers, sold under thetrade names ECOFLEX and EASTAR BIO, respectively. Bayer has developedpolyesteramides under the trade name BAK. Du Pont has developed BIOMAX,a modified polyethylene terephthalate (PET). Cargill-Dow has sold avariety of biopolymers based on polylactic acid (PLA). Monsantodeveloped a class of polymers known as polyhydroxyalkanoates (PHA),which include polyhydroxybutyrates (PHB), polyhydroxyvalerates (PHV),and polyhydroxybutyrate-hydroxyvalerate copolymers (PHBV). Union Carbidemanufactures polycaprolactone (PCL) under the trade name TONE.

Each of the foregoing biopolymers has unique properties, benefits andweaknesses. For example, biopolymers such as BIOMAX, BAK, PHB and PLAtend to be strong but are also quite rigid or even brittle. This makesthem poor candidates when flexible sheets or films are desired, such asfor use in making wraps, bags and other packaging materials requiringgood bend and folding capability. In the case of BIOMAX, DuPont does notpresently provide specifications or conditions suitable for blowingfilms therefrom, thus indicating that it may not be presently believedthat films can be blown from BIOMAX and similar polymers.

On the other hand, biopolymers such as PHBV, ECOFLEX and EASTAR BIO aremany times more flexible compared to the more rigid biopolymersdiscussed immediately above. However, they have relatively low meltingpoints such that they tend to be self adhering and unstable when newlyprocessed and/or exposed to heat. While initially easily blown intofilms, such films are often difficult to process on a mass scale sincethey will tend to self adhere when rolled onto spools, which istypically required for sale and transport to other locations andcompanies. To prevent self-adhesion (or “blocking”) of such films, it istypically necessary to incorporate a small amount (e.g. 0.15% by weight)of silica, talc or other fillers.

Another important criteria for sheets and films used in packaging istemperature stability. “Temperature stability” is the ability tomaintain desired properties even when exposed to elevated or depressedtemperatures, or a large range of temperatures, which may be encounteredduring shipping or storage. For example, many of the more flexiblebiopolymers tend to become soft and sticky if heated significantly aboveroom temperature, thus compromising their ability to maintain theirdesired packaging properties. Other polymers can become rigid andbrittle upon being cooled significantly below freezing (i.e., 0° C.).Thus, certain homopolymers or copolymers may not by themselves havesufficient stability within large temperature ranges.

In the case of the packaging of foods, such as refrigerated meats orfast foods, the packaging materials may be subjected to widelyfluctuating temperatures, often being exposed to rapid changes intemperature. A biopolymer that may be perfectly suitable at roomtemperature, for example, may become completely unsuitable when used towrap hot foods, particularly foods that emit significant quantities ofhot water vapor or steam. In the case of meats, a wrapping that may besuitable when used at room temperature or below, such as atrefrigeration or freezing temperatures, might become soft and stickyduring microwave thawing of the meat. Of course, it would generally beunacceptable for a biopolymer to melt or adhere to the meat or fast foodbeing served unless it was desired for some reason that the personactually consume the biopolymer.

Another factor that impacts whether a particular material is suitablefor use as a wrap (e.g. sandwich or meat wrap) is whether sheets orfilms formed therefrom have suitable “dead-fold” properties. The term“dead-fold” is a measurement of the tendency of a sheet or film toremain in a desired orientation once used to encapsulate, enclose, wrapor otherwise enclose at least a portion of an item to be packaged. Wrapsmade from paper, for example, typically have modest to excellent deadfold properties depending on how the paper has been processed ortreated. On the other hand, many plastic films or sheets (e.g.polyethylene) have very poor dead-fold properties such that they makevery poor wraps. Instead, they are better suited for other uses, such assacks, bags, pouches, coverings, etc. where good dead-fold is notnecessary or desirable. In order to compensate for generally poordead-fold properties, plastic wraps are typically manufactured to havehigh self-cling (e.g. SARAN WRAP). Self cling is a property havinglittle to do with dead-fold, and is akin to the use of adhesives. Oneproblem with self cling wraps is that they can be very difficult tohandle. A self-cling wrap that is accidentally allowed to cling toitself before being used to wrap the substrate becomes useless and mustbe discarded and replaced with another length of self-cling wrap.

Paper also breathes (i.e. transmits gas) and has good water vaportransmission unless completely sealed with a wax or plastic. Plasticfilms and sheets, on the other hand, generally have very poor watervapor transmission and breathability. As a result, paper is a muchbetter as a wrap for hot foods than plastic sheets because it permitsthe escape of water vapor. A plastic sheet, on the other hand, willretain virtually all of the water vapor, which condenses over time onthe plastic surface and can make the food soggy, particularly a bun orslice of bread.

In view of the foregoing, it would be an advancement in the art toprovide biodegradable polymers which could be readily formed into sheetsand films that had strength and flexibility properties suitable for useas packaging materials and that had suitable temperature stability for agiven use. In addition or alternatively, it would also be an advancementin the packaging art to provide improved biodegradable polymers thatcould be formed into sheets and films having sufficient dead-fold sothat they could be folded, wrapped or otherwise manipulated in order toreliably enclose a substrate therein. In addition or alternatively, itwould be a further advancement in the packaging art to provide improvedbiodegradable sheets and films that had enhanced breathability and watervapor transmission compared to conventional plastic sheets.

Such improved biopolymers, as well as sheets and films formed therefrom,are disclosed and claimed herein.

SUMMARY OF THE INVENTION

The invention encompasses biodegradable polymer blends having improvedproperties, including one or more of increased strength, flexibility,elongation, temperature stability, processability, breathability anddead-fold. Such polymer blends may be extruded, blown, cast or otherwiseformed into sheets and films for use in a wide variety of packagingmaterials, such as wraps, bags, pouches, and laminate coatings, or theymay be molded into shaped articles. In many cases, existing mixing,extrusion, blowing, injection molding, and blow molding apparatus knownin the thermoplastic art are perfectly suitable for use in forminguseful articles of manufacture, including sheets and films, from thethermoplastic compositions described herein.

One aspect of the invention involves blending at least one biopolymerhaving relatively high stiffness with at least one biopolymer havingrelatively high flexibility. For example, blends containing a relativelystiff BIOMAX polymer, a modified PET sold by Du Pont, with a relativelysoft or flexible ECOFLEX, an aliphatic-aromatic copolymer sold by BASF,and/or EASTAR BIO, an aliphatic-aromatic copolymer sold by EastmanChemical, have been shown to have strength and elongation propertieswhich are superior to either biopolymer taken alone. Thus, the presentinvention provides blends that possess or demonstrate surprisingsynergistic effects.

BIOMAX is characterized as having a relatively high glass transitiontemperature and is highly crystalline at room temperature. BIOMAX tendsto be quite stiff or brittle when formed into films or sheets. It alsohas poor elongation or elasticity. ECOFLEX, on the other hand, ischaracterized as having a relatively low glass transition temperatureand is relatively amorphous or noncrystalline at room temperature, allof which contribute to the high softness, elasticity and high elongationof ECOFLEX. Even so, the inventors have discovered the surprising andunexpected result that various blends of BIOMAX and ECOFLEX actuallyexhibit higher elongation than ECOFLEX by itself, as well as higherbreak stress compared to either BIOMAX or ECOFLEX by themselves.

Other polymer blends have been developed, including but not limited to,a blend of ECOFLEX, PLA and thermoplastic starch (TPS) and a blend ofBAK and TPS. In each case, blending a biopolymer having a relatively lowglass transition temperature with a biopolymer having a relatively highglass transition temperature has resulted in polymer blends that, inmany cases, exhibit the desired characteristics of each polymer byitself, in some cases exhibiting even better properties, whilediminishing or minimizing the negative properties of each biopolymer byitself.

In general, biopolymers that may be characterized as being relatively“stiff” or less flexible include polymers which have a glass transitiontemperature greater than about 10° C., while biopolymers that may becharacterized as being relatively “soft” include polymers having a glasstransition temperature less than about 0° C. “Stiff” biopolymerspreferably have a glass transition temperature greater than about 15°C., more preferably greater than about 25° C., and most preferablygreater than about 35° C. “Soft” biopolymers preferably have a glasstransition temperature of less than about −4° C., more preferably lessthan about −10° C., more especially preferably less than about −20° C.,and most preferably less than about −30° C.

In addition, “stiff” polymers are generally more crystalline, while“soft” polymers are generally less crystalline and more amorphous,particularly at room temperature.

The relatively stiff polymers, characterized as those polymers generallyhaving a glass transition greater than about 10° C., will preferablyhave a concentration in a range from about 20% to about 99% by weight ofthe biodegradable polymer blend, more preferably in a range from about55% to about 98% by weight, and most preferably in a range from about70% to about 95% by weight of the polymer blend (i.e., the combinedweight of the stiff and soft polymers).

The relatively soft polymers, characterized as those polymers generallyhaving a glass transition less than about 0° C., will preferably have aconcentration in a range from about 1% to about 80% by weight of thebiodegradable polymer blend, more preferably in a range from about 2% toabout 45% by weight, and most preferably in a range from about 5% toabout 30% by weight of the polymer blend.

Biopolymers within the scope of the present invention include, but arenot limited to, synthetic polyesters, semi-synthetic polyesters made byfermentation (e.g., PHB and PHBV), polyester amides, polycarbonates, andpolyester urethanes. In another aspect, it is within the scope of theinvention to optionally include a variety of natural polymers and theirderivatives, such as polymers comprising or derived from starch,cellulose, other polysaccharides and proteins.

Although it is within the scope of the invention to includethermoplastic polymers based on starch that include a high boilingliquid plasticizer such as glycerine, propylene glycol and the like, itis preferable, when manufacturing wraps that are intended to come intocontact with food products, to utilize thermoplastic starch polymersthat are made without the use of such plasticizers, which canpotentially diffuse into food. Preferred thermoplastic starch polymersfor use in making food wraps may advantageously utilize the naturalwater content of native starch granules to initially break down thegranular structure and melt the native starch. Thereafter, the meltedstarch can be blended with one or more synthetic biopolymers, and themixture dried by venting, in order to yield a final polymer blend. Whereit is desired to make food wraps or other sheets or films intended tocontact food using a thermoplastic starch polymer made with a highboiling liquid plasticizer, it will be preferable to limit the quantityof such thermoplastic starch polymers to less than 10% by weight of thepolymer mixture, exclusive of any solid fillers.

In another aspect, it is within the scope of the invention to includeone or more nonbiodegradable polymers within the polymer blends. Suchpolymers may remain in particulate form, or they may becomethermoplastic during processing. In either case, the resulting polymerblends will tend to exhibit biodegradability so long as thenonbiodegradable polymers are included as a disperse, rather than acontinuous, phase.

In another aspect, it is within the scope of the invention toincorporate inorganic and organic fillers in order to decreaseself-adhesion, lower the cost, and increase the modulus of elasticity(Young's modulus) of the polymer blends. Examples of inorganic fillersinclude calcium carbonate, titanium dioxide, silica, talc, mica, and thelike. Examples of organic fillers include wood flour, seeds, polymericparticles, ungelatinized starch granules, and the like. In addition,plasticizers may be used in order to impart desired softening andelongation properties.

In the case of sheets or films intended to be used as “wraps”, such aswraps used to enclose meats, other perishable food items, and especiallyfast food items (e.g., sandwiches, burgers and dessert items), it may bedesirable to provide sheets and films having good “dead-fold” propertiesso that once folded, wrapped or otherwise manipulated into a desiredorientation, such wraps will tend to substantially maintain theirorientation so as to not spontaneously unfold or unwrap, as occurs witha large number of plastic sheets and films (e.g., polyethylene).Dead-fold is a measure of the ability of a sheet or film to retain acrease, crinkle or other bend. It is measured independently of selfcling, heat sealing, or the use of an adhesive to maintain a desiredorientation.

In order to improve the dead-fold properties of sheets or films producedtherefrom, biopolymer blends (optionally including fillers) may beengineered so as to yield films having a relatively high Young'smodulus, preferably greater than about 100 MPa, more preferably greaterthan about 150 MPa, and most preferably greater than about 200 MPa. Ingeneral, increasing the concentration of the stiff biopolymer will tendto increase the Young's modulus and the resulting dead-fold properties.It should be understood, however, that Young's modulus only looselycorrelates to dead-fold and does not, in every case, serve to define orpredict the dead-fold properties of a particular sheet or film.

Including an inorganic filler is another way to increase dead-fold.Thus, it has been found that adding significant quantities of aninorganic filler, such as greater than about 10% by weight of theoverall mixture, preferably greater than about 15% by weight, morepreferably greater than about 20% by weight, more especially preferablygreater than about 30% by weight, and most preferably greater than about35% by weight of the overall mixture, greatly improves the dead-foldproperties of sheets and films manufactured from polymers or polymerblends according to the invention.

Yet another way to increase the dead-fold properties is to increase thesurface area, or “bulk hand feel” of a sheet, which is done bydisrupting the generally smooth, planar nature of the sheet or film.This may be accomplished, for example, by embossing, crimping, quiltingor otherwise texturing the sheet so as to have regularly spaced-apart orrandom hills and valleys rather than simply being a perfectly smooth,planar sheet. A sheet or film may be textured, for example, by passingthe sheet or film through a pair of knurled or other embossing-typerollers. Such texturing increases the ability of a sheet to take andmaintain a fold, thus improving the dead-fold properties of the sheet.Another way to increase the surface area of sheets and films accordingto the invention is to incorporate one or more particulate fillers that,at least a portion of which, have a particle size diameter equal to orgreater than the thickness of the film or sheet.

When used to wrap foods, or whenever good dead-fold properties aredesired, sheets and films according to the invention can be manufacturedso as to have a dead-fold of at least about 50% (i.e., when creasedusing a standard dead-fold test, the sheets and films will maintain atleast about 50% of their original crease). Preferably, such sheets andfilms will have a dead-fold greater than about 60%, more preferablygreater than about 70%, and most preferably greater than about 80%. Aswill be shown hereafter, sheets and films according to the inventionhave been developed that have a dead-fold approaching or equal to 100%(i.e., when folded they remain folded absent the application of anexternal force sufficient to reverse the fold). By way of comparison,sheets and films made from polyethylene (e.g., for use in makingsandwich or garbage bags) typically have a dead-fold of 0%. Standardpaper wraps commonly used in the fast food industry typically have adead-fold between about 40-80%. Thus, sheets and films according to theinvention have dead-fold properties that meet or exceed those ofstandard paper wraps, and which are many times greater than conventionalplastic films and sheets, often orders of magnitude greater.

In some cases, it may be desirable for sheets and films according to theinvention to have the feel and breathability of paper. As set forthabove, particulate fillers, both organic and inorganic, can be used toincrease the modulus of elasticity and dead-fold. Such fillers alsoadvantageously create “cavitation” whenever the sheets or films arestretched during processing. Cavitation occurs as the thermoplasticpolymer fraction is pulled in either a monoaxial or biaxial directionand the filler particles create a discontinuity in the film or sheetthat increases in size during stretching. In essence, a portion of thestretched polymer pulls away from the filler particles, resulting intiny cavities in the vicinity of the filler particles. This, in turn,results in greatly increased breathability and vapor transmission of thesheets and films. It also results in films or sheets having a touch andfeel that much more closely resembles the touch and feel of paper, ascontrasted with conventional thermoplastic sheets and films. The resultis a sheet or wrap that can be used for applications that are presentlyperformed or satisfied using paper products (i.e., wraps, tissues,printed materials, etc.)

Articles of manufacture made according to the invention can have anydesired thickness. Thicknesses of sheets and films may range from0.0001″ to 0.1″ (about 2.5 microns to about 2.5 mm). Sheets and filmssuitable for wrapping, enclosing or otherwise covering food items orother solid substrates will typically have a measured thickness betweenabout 0.0003 ″ and about 0.01″ (about 7.5-250 microns), and a calculatedthickness between about 0.00015″ and about 0.005″ (about 4-125 microns).The measured thickness will typically be between 10-100% larger than thecalculated thickness when the sheets and films are made fromcompositions that have a relatively high concentration of particulatefiller particles, which can protrude from the surface of the sheet orfilm. This phenomenon is especially pronounced when significantquantities of filler particles having a particle size diameter that islarger than the thickness of the polymer matrix are used.

Another advantage of utilizing biopolymers in the manufacture of wrapsis that biopolymers are generally able to accept and retain print muchmore easily than conventional plastics or waxed papers. Many plasticsand waxes are highly hydrophobic and must be surface oxidized in orderto provide a chemically receptive surface to which ink can adhere.Biopolymers, on the other hand, typically include an abundant fractionof oxygen-containing moieties, such as ester, amide and/or urethanegroups, to which inks can readily adhere.

The sheets and films according to the invention may comprise a singlelayer or multiple layers as desired. They may be formed by mono- andco-extrusion, casting and film blowing techniques known in the art.Because they are thermoplastic, the sheets can be post-treated by heatsealing to join two ends together to form sacks, pockets, pouches, andthe like. They can be laminated onto existing sheets or substrates. Theycan also be coated themselves.

These and other features of the present invention will become more fullyapparent from the following description and appended claims, or may belearned by the practice of the invention as set forth hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the manner in which the above-recited and other advantagesand objects of the invention are obtained, a more particular descriptionof the invention briefly described above will be rendered by referenceto a specific embodiment thereof which is illustrated in the appendeddrawings. Understanding that these drawings depict only a typicalembodiment of the invention and are not therefore to be considered to belimiting of its scope, the invention will be described and explainedwith additional specificity and detail through the use of theaccompanying drawings, in which:

FIG. 1 is a plot of the percent elongation at break versus the appliedstrain rate for various neat and blended polymer films;

FIG. 2 is a plot of the percent elongation of various neat polymer andblended polymer films versus the concentration of ECOFLEX within thefilms at a fixed strain rate of 500 mm/min.;

FIG. 3 is a plot of the percent elongation of various neat polymer andblended polymer films versus the concentration of ECOFLEX within thefilms at a fixed strain rate of 1000 mm/min.;

FIG. 4 is a plot of the break stress versus the applied strain rate forvarious neat and blended polymer films;

FIG. 5 is a plot of the break stress of various neat polymer and blendedpolymer films versus the concentration of ECOFLEX within the films at afixed strain rate of 500 mm/min.;

FIG. 6 is a plot of the break stress of various neat polymer and blendedpolymer films versus the concentration of ECOFLEX within the films at afixed strain rate of 1000 mm/min.;

FIG. 7 is a plot of the Water Vapor Permeability Coefficients (WVPC) ofvarious neat polymer and blended polymer films as a function of theconcentration of ECOFLEX within the films, and an estimated trend linebased on the lowest measured WVPC for a neat ECOFLEX film of 7.79×10⁻³g·cm/m²/d/mm Hg.;

FIG. 8 is a plot of the Water Vapor Permeability Coefficients (WVPC) ofvarious neat polymer and blended polymer films as a function of theconcentration of ECOFLEX within the films, and an estimated trend linebased on the highest measured WVPC for a neat ECOFLEX film of 42×10⁻³g·cm/m²/d/mm Hg.; and

FIG. 9 is a plot of the modulus of various neat polymer and blendedpolymer films versus the concentration of ECOFLEX within the films.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS I. Introduction

The invention relates to biodegradable polymer blends having greatlyimproved properties compared to unblended and/or unfilled biodegradablehomopolymers and copolymers. Such properties include one or more ofimproved strength, flexibility, elongation, temperature stability,processability, and dead-fold. Moreover, sheet, films and other articlesmade from such blends are in many ways superior to conventionalplastics, which suffer from their inability to degrade when discarded inthe environment, which are not readily printable absent specialtreatment, and which generally have poor dead-fold properties.

In one aspect of the invention, polymer blends according to theinvention may include at least one biopolymer having relatively highstiffness and at least one biopolymer having relatively highflexibility. When blended together, it is possible to derive thebeneficial properties from each polymer while offsetting or eliminatingthe negative properties of each polymer when used separately to makefilms, sheets and other articles.

The inventive polymer blends may be extruded, blown or otherwise formedinto sheets and films for use in a wide variety of packaging materials,such as wraps, bags, pouches, coverings, and laminate coatings. Byblending a relatively stiff polymer with a relatively flexible polymer,the inventors have discovered that, in some cases, the beneficialproperties of the blend actually exceed the desirable properties of eachpolymer when used individually. Thus, the surprising result of anunexpected synergistic effect has been demonstrated.

Biopolymers that may be used within blends within the scope of thepresent invention include, but are not limited to, synthetic polyesters,naturally derived polyesters, polyester amides, polycarbonates, andpolyester urethanes, but may also include a variety of natural polymersand their derivatives, such as polymers and derivatives of starch,cellulose, other polysaccharides, and proteins. Particulate fillers,both organic and inorganic, may be incorporated to improve the dead-foldproperties, increase bulk hand feel, reduce cost, and decreaseself-adhesion. Plasticizers may be added to impart desired softening andelongation properties. Sheets and films may be embossed, crimped,quilted or otherwise textured to improve bulk hand feel and dead-fold.The biopolymers and biopolymer blends according to the invention morereadily accept and retain print compared to conventional plastics orwaxed papers because they typically include oxygen-containing moieties,such as ester, amide, or urethane groups, to which inks can readilyadhere.

The terms “sheets” and “films” are to be understood as having theircustomary meanings as used in the thermoplastic and packaging arts.Nevertheless, because the distinction between what constitutes a “sheet”and what constitutes a “film” largely turns on the thickness of thearticle of manufacture, the distinction is somewhat arbitrary (i.e. somearticles may constitute both sheets and films). Because thebiodegradable compositions according to the invention can be used tomanufacture a wide variety of articles of manufacture, includingarticles useful to wrap, package or otherwise package food or othersolid substrates, including sheets and films having a wide variety ofthicknesses (both measured and calculated), it is not the intention ofthis disclosure to precisely distinguish, in all cases, between what mayarguably constitute a “sheet” versus articles that may arguablyconstitute a “film”. Therefore, when the present disclosure refers to“sheets and films” and “sheets or films”, the intention is to designatethe entire universe of articles of manufacture that may arguablyconstitute “sheets”, “films” or both.

The term “polymer blend” includes two or more unfilled polymers and/orone or more polymers into which one or more types of solid fillers havebeen added.

II. Biodegradable Polymers

Biopolymers within the scope of the present invention include polymerswhich degrade through the action of living organisms, light, air, waterand combinations of the foregoing. Such polymers include a range ofsynthetic polymers, such as polyesters, polyester amides, polycarbonatesand the like. Naturally-derived semi-synthetic polyesters (e.g. fromfermentation) can also be used. Biodegradation reactions are typicallyenzyme-catalyzed and generally occur in the presence of moisture.Natural macromolecules containing hydrolyzable linkages, such asprotein, cellulose and starch, are generally susceptible tobiodegradation by the hydrolytic enzymes of microorganisms. A fewman-made polymers, however, are also biodegradable. Thehydrophilic/hydrophobic character of polymers greatly affects theirbiodegradability, with more polar polymers being more readilybiodegradable as a general rule. Other important polymer characteristicsthat affect biodegradability include crystallinity, chain flexibilityand chain length.

Besides being able to biodegrade, it is often important for a polymer orpolymer blend to exhibit certain physical properties, such as stiffness,flexibility, water-resistance, strength, elongation, temperaturestability, moisture vapor transmission, gas permeability, and/ordead-fold. The intended application of a particular polymer blend willoften dictate which properties are necessary in order for a particularpolymer blend, or article manufactured therefrom, to exhibit the desiredperformance criteria. In the case of sheets and films suitable for useas packaging materials, desired performance criteria may includeelongation, dead-fold, strength, printability, imperviousness toliquids, breathability, temperature stability, and the like.

Because of the limited number of biodegradable polymers, it is oftendifficult, or even impossible, to identify one single polymer orcopolymer which meets all, or even most, of the desired performancecriteria for a given application. This is particularly true in the areaof packaging materials. Polymers that have a high glass transitiontemperature (T_(g)) are often difficult, if not impossible, to blow orcast into films on a mass scale. On the other hand, polymers that have avery low glass transition temperature typically have relatively lowsoftening and/or melting points, which makes them difficult to massproduce into sheets and films without the tendency of blocking, or selfadhesion. Moreover, such sheets and films may lack adequate strength,water vapor barrier properties, high temperature stability, and/ormodulus to be suitable for certain applications, such as in themanufacture of wraps or laminates coatings.

For these and other reasons, biodegradable polymers have found littleuse in the area of food packaging materials, particularly in the fieldof wraps used to package and encapsulate food items during singleserving use. In one aspect of the invention, the inventors havediscovered that sheets and films suitable for making wraps and otherpackaging materials can be obtained by blending one or more “stiff”, orhigh glass transition temperature, polymers with one or more “soft”, orlow glass transition temperature, polymers. In another aspect of theinvention, polymers or polymer blends can be filled with particulatefillers, and/or sheets or films made therefrom can be textured, in orderto yield sheets have adequate dead-fold properties.

A. Stiff Polymers.

Even though the use of terms such as “stiff” and “soft” polymers may besomewhat arbitrary, such classifications are useful when determiningwhich polymers to blend together in order to obtain a polymer blendhaving the desired performance criteria, particularly when the goal isto manufacture a film or sheet suitable for use as a laminate coating,such as on molded articles made of starch or other moisture sensitivematerials, or as a wrap or other packaging material.

In general, those polymers that may be characterized as being relatively“stiff”, or less flexible, typically include polymers which have a glasstransition temperature greater than about 10° C. Stiff polymers withinthe scope of the invention will preferably have a glass transitiontemperature greater than about 15° C., more preferably greater thanabout 25° C., and most preferably greater than about 35° C. Theforegoing ranges attempt to take into consideration the fact that the“glass transition temperature” is not always a discreet temperature butis often a range of temperatures within which the polymer changes frombeing a glassy and more brittle material to being a softer and moreflexible material.

The glass transition temperature should be distinguished from themelting point of a polymer, at or beyond which a thermoplastic polymerbecomes plastic and deformable without significant rupture. Althoughthere is often a positive correlation between a polymer's glasstransition temperature (T_(g)) and its melting point (T_(m)), this isnot strictly the case with all polymers. In some cases the differencebetween T_(g) and T_(m) may be large. In other cases it may berelatively small. It is generally the case, however, that the meltingpoint of a stiffer polymer will typically be greater than the meltingpoint of a softer polymer.

Preferred “stiff” polymers within the scope of the present inventioninclude, but are not limited to, modified polyethylene terephthalates(such as those manufactured by Du Pont), polyesteramides (such as thosemanufactured by Bayer), polylactic acid-based polymers (such as thosemanufactured by Cargill-Dow Polymers and Dianippon Ink), terpolymersbased on polylactic acid, polyglycolic acid and polycaprolactone (suchas those manufactured by Mitsui Chemicals), polyalkylene carbonates(such as polyethylene carbonate manufactured by PAC Polymers), andpolyhydroxybutyrate (PHB).

A presently preferred stiff biopolymer within the scope of the inventionincludes a range of modified polyethylene terephthalate (PET) polymersmanufactured by DuPont, and sold under the trade name BIOMAX. Variousmodified PET polymers of DuPont are described in greater detail in U.S.Pat. No. 5,053,482 to Tietz, U.S. Pat. No. 5,097,004 to Gallagher etal., U.S. Pat. No. 5,097,005 to Tietz, U.S. Pat. No. 5,171,308 toGallagher et al., U.S. Pat. No. 5,219,646, to Gallagher et al., and U.S.Pat. No. 5,295,985 to Romesser et al. For purposes of disclosing “stiff”polymers, the foregoing patents are disclosed herein by reference.

In general, the modified PET polymers of DuPont may be characterized ascomprising alternating units of terephthalate and an aliphaticconstituent, with the aliphatic constituent comprising a statisticaldistribution of two or more different aliphatic units derived from twoor more different diols, such as ethylene glycol, diethylene glycol,triethylene oxide, polyethylene glycol, lower alkane diols, bothbranched and unbranched, and derivatives of the foregoing. A portion ofthe aliphatic units may also be derived from an aliphatic diacid, suchas adipic acid. In addition, a fraction of the phenylene groups withinthe repeating terephthalate units may be sulfonated and neutralized withan alkali metal or alkaline earth metal base. Both the aliphatic portionof the modified PET polymer as well as the statistically significantquantity of sulfonated terephthalate units contribute significantly tothe biodegradability of the BIOMAX polymer.

Some BIOMAX grades of polymers have a melting point of 200-208° C. and aglass transition temperature of 40-60° C. BIOMAX 6926 is one such grade.It is a relatively strong and stiff polymer that, when blended with asofter polymer, yields excellent sheets and films suitable for wrappingand other packaging materials. Films and sheets of BIOMAX or BIOMAXblends can be cast or blown and then optionally textured in order toimpart desired properties described more fully herein. In addition, orin the alternative, one or more particulate fillers may be included inorder to impart desired properties described more fully herein.

In general, modified polyethylene terephthalates that would be expectedto have properties suitable for use as a “stiff” biodegradable polymerconsist essentially of recurring structural units having the followinggeneral formula:—[—C(O)—R—C(O)—OGO—]_(a)—[—C(O)-Q-O—]_(b)—

-   -   wherein up to about 40 mole % of R is selected from the group        consisting of a chemical bond and one or more divalent,        non-aromatic, C₁-C₁₀ hydrocarbylene radicals, and the remainder        of R is at least about 85% mole % p-phenylene radical,    -   wherein G includes from 0 to about 30 mole % of a polyethylene        ether radical selected from the group consisting of:        —(CH₂)₂—O—(CH₂)₂—and —(CH₂)₂—O—(CH₂)₂—O—(CH₂)₂—        and the remainder of G is selected from the group consisting of        polyalkylene ether radicals of molecular weight at least about        250 (number average), and —(CH₂)₂—, —(CH₂)₃—, and —(CH₂)₄—        radicals,    -   wherein Q is derived from a hydroxy acid of the formula:        HO[—C(O)-Q-O—]_(x)H    -   wherein x is an integer and such hydroxy acids have a melting        point at least 5° C. below their decomposition temperature, and        Q is selected from the group consisting of a chemical bond and        hydrocarbylene radicals —(CH₂)_(n)—, where n is an integer from        1 to 5, —C(R′)H—, and —C(R′)HCH₂—. wherein R′ is selected from        the group consisting of —CH₃ and —CH₂CH₃, and wherein “a” and        “b” are mole fractions of the polymer, and the mole fraction “a”        may be 0.6 to 1 and, correspondingly, mole fraction “b” may be 0        to 0.4, and wherein about 0.1 to about 15 mole %, preferably        about 0.1 to about 2.5 mole %, of the polymer contains alkali        metal or alkaline earth metal sulfo groups, especially about 1.5        to about 2 mole % of such groups.

Another stiff biopolymer that may be used in manufacturing polymerblends according to the present invention includes polylactic acid(PLA). Polylactic acid typically has a glass transition temperature ofabout 59° C. and a melting point of about 178° C. PLA has low elongationand is quite hard. It is a strong thermoplastic material that can beinjection molded, extruded, cast, thermoformed, or used as spun ormelt-blown fibers to produce nonwoven goods.

Polymers based on or including PLA first found commercial application asmedical sutures in 1970. High polymers of lactic acid(M_(n)=50,000-110,000) are strong thermoplastics that can be fabricatedinto useful products that can be broken down by common soil bacteria.Potential applications of PLA include paper coatings for packaging (foodand beverage cartons), plastic foam for fast foods, microwavablecontainers, and other consumer products such as disposable diapers oryard waste bags. PLA can be a homopolymer or it may be copolymerizedwith glycolides, lactones or other monomers. One particularly attractivefeature of PLA-based polymers is that they are derived from renewableagricultural products.

Because lactic acid is difficult to polymerize directly to high polymersin a single step on a commercial scale, most companies employ a two-stepprocess. Lactic acid is first oligomerized to a linear chain with amolecular weight of less than 3000 by removing water. The oligomer isthen depolymerized to lactide, which is a cyclic dimer consisting of twocondensed lactic acid molecules. This six-member ring is purified andsubjected to ring opening polymerization to produce polylactic acid witha molecular weight of 50,000-110,000.

Because lactic acid has an asymmetric carbon atom, it exists in severalisomeric forms. The lactic acid most commonly sold commercially containsequal parts of L-(+)-lactic acid and D-(−)-lactic acid and is thereforeoptically inactive, with no rotatory power. The racemic mixture iscalled DL-lactic acid.

Another stiff polymer that may be used within the inventive polymerblends is known as CPLA, which is a derivative of PLA and is sold byDianippon Ink. Two classes of CPLA are sold and are referred to as “CPLAhard” and “CPLA soft”, both of which comprise “stiff polymers”, as thatterm has been defined herein. CPLA hard has a glass transitiontemperature of 60° C., while CPLA soft has a glass transitiontemperature of 51° C.

Bayer corporation manufactures polyesteramides sold under the name BAK.Polyester amides manufactured by Bayer are described more fully in U.S.Pat. No. 5,644,020 to Timmermann et al. For purposes of disclosingbiodegradable polymers, at least some of which constitute “stiff”polymers, the foregoing patent is incorporated herein by reference. Oneform of BAK is prepared from adipic acid, 1,4-butanediol, and6-aminocaproic acid. BAK 1095, a polyesteramide having an M_(n) of22,700 and an M_(w) of 69,700 and which contains aromatic constituents,has a melting point of 125° C. BAK 2195 has a melting point of 175° C.Although the glass transition temperatures of BAK 1095 and BAK 2195 aredifficult to measure, because BAK appears to behave like a stiff polymerin the sense that improved properties may be obtained by blending BAKwith a soft polymer, the inventors believe that the glass transitiontemperature of BAK polymers is essentially at least about 10° C. Forpurposes of understanding the meaning and scope of the specification andclaims, polyester amides such as BAK, as well as others that behave likeBAK and can be used as a “stiff” polymer, shall be deemed to have aglass temperature of at least about 10° C.

Mitsui Chemicals, Inc. manufactures a terpolymer that includes unitsderived from polylactide, polyglycolide and polycaprolactone that havebeen condensed together. Thus, this polymer is an aliphatic polymer andmay be characterized as a PLA/PGA/PCL terpolymer. Three grade of thispolymer are available, H100J, S100 and T100. The H100J grade PLA/PGA/PCLterpolymer has been analyzed to have a glass transition temperatures of74° C. and a melting point of 173° C.

PAC Polymers Inc. manufactures polyethylene carbonate (PEC) having aglass transition temperature range of 10-28° C. PEC is a “stiff” polymerfor purposes of the present invention.

Polyhydroxybutyrates (PHBs) can act as either a stiff or soft polymerdepending on their molecular weight, whether they have been modifiedusing chain extenders and/or branching agents, whether they have beencopolymerized with another polymer, and depending on the otherconstituents within the overall thermoplastic composition. In thissense, PHBs are unique among biopolymers and may be of special interestfor use in making wraps, laminate coatings, packaging materials, and thelike.

As discussed more fully below, native or dried gelatinized starch can beused as particulate fillers in order to increase the dead-foldproperties of sheets and films made from a particular polymer or polymerblend. However, to the extent that starches become thermoplastic butretain a substantial portion of their crystallinity, such starches mayact as “stiff”, rather than “soft”, polymers.

B. Soft Polymers.

In general, those biopolymers that may be characterized as being “soft”,or less rigid, typically include polymers which have a glass transitiontemperature of less than about 0° C. Soft biopolymers within the scopeof the invention will preferably have a glass transition temperature ofless than about −4° C., more preferably less than about −10° C., moreespecially preferably less than about −20° C., and most preferably lessthan about −30° C. The foregoing ranges attempt to take intoconsideration the fact that the “glass transition temperatures” of“soft” polymers are not always discreet temperatures but often comprisea range of temperatures.

Preferred “soft” biopolymers within the scope of the present inventioninclude, but are not limited to, aliphatic-aromatic copolyesters (suchas those manufactured by BASF and Eastman Chemical), aliphaticpolyesters which include repeating units having at least 5 carbon atoms,e.g., polyhydroxyvalerate, polyhydroxybutyrate-hydroxyvalerate copolymerand polycaprolactone (such as those manufactured by Daicel Chemical,Monsanto, Solvay, and Union Carbide), and succinate-based aliphaticpolymers, e.g., polybutylene succinate (PBS), polybutylene succinateadipate (PBSA), and polyethylene succinate (PES) (such as thosemanufactured by Showa High Polymer).

U.S. Pat. No. 5,817,721 to Warzelhan et al., and assigned to BASF,discloses a range of aliphatic-aromatic copolyesters within the scope ofthe invention. Similarly, U.S. Pat. Nos. 5,292,783, 5,446,079,5,559,171, 5,580,911, 5,599,858 and 5,900,322, all to Buchanan et al.and assigned to Eastman Chemical, as well as U.S. Pat. Nos. 6,020,393and 6,922,829 to Khemani, also assigned to Eastman Chemical, alldisclose aliphatic-aromatic copolyesters within the scope of theinvention. For purposes of disclosing “soft” polymers, the foregoingpatents are incorporated herein by reference.

A preferred “soft” polymer that may be used in the manufacture of theinventive polymer blends includes aliphatic-aromatic copolyestersmanufactured by BASF and sold under the trade name ECOFLEX. Thealiphatic-aromatic copolyesters manufactured by BASF comprise astatistical copolyester derived from 1,4-butanediol, adipic acid, anddimethylterephthalate (DMT). In some cases, a diisocyanate is used as achain lengthener. Branching agents may also be used to yield branched,rather than linear, copolymers.

Copolymerization of aliphatic monomers, such as diols and diacids, witharomatic monomers, such as diols and diacids (e.g., terephthalic acid ordiester derivatives such as DMT), is one way to improve the performanceproperties of aliphatic polyesters. However, questions have been raisedwithin the industry regarding the complete biodegradability ofaliphatic-aromatic copolyesters because aromatic copolyesters such asPET are known to be resistant to microbial attack. Nevertheless,researchers have discovered that aliphatic-aromatic copolyesters areindeed biodegradable and that the biodegradability of these copolyestersis related to the length of the aromatic sequence. Block copolyesterswith relatively long aromatic sequences are less rapidly degraded bymicroorganisms compared to random copolyesters having more interruptedaromatic sequences. Film thickness is also a factor, with thicker filmsdegrading more slowly due to their reduced surface to volume ratio thanthinner films, all things being equal. The polymer presently sold underthe name ECOFLEX S BX 7000 by BASF has a glass transition temperature of−33° C. and a melting range of 105-115° C.

Another “soft” aliphatic-aromatic copolyester is manufactured by EastmanChemical Company and is sold under the trade name EASTAR BIO. Thealiphatic-aromatic copolyester manufactured by Eastman is a randomcopolymer derived from 1,4-butanediol, adipic acid, anddimethylterephthalate (DMT). One particular grade of EASTAR BIO, knownas EASTAR BIO 14766, has a glass transition temperature of −33° C. and amelting point of 112° C. It has a tensile strength at break in themachine direction of 19 MPa, an elongation at break of 600%, and atensile modulus of elasticity of 97 MPa (tangent). It has an Elmendorftear strength of 282 g.

Polycaprolactone (PCL) is a biodegradable aliphatic polyester having arelatively low melting point and a very low glass transitiontemperature. It is so named because it is formed by polymerizing∈-caprolactone. The glass transition temperature of PCL is −60° C. andthe melting point is only 60° C. Because of this, PCL and other similaraliphatic polyesters with low melting points are difficult to process byconventional techniques such as film blowing and blow molding. Filmsmade from PCL are tacky as extruded and have low melt strength over 130°C. Also, the slow crystallization of this polymer causes the propertiesto change over time. Blending PCL with other polymers improves theprocessability of PCL. One common PCL is TONE, manufactured by UnionCarbide. Other manufactures of PCL include Daicel Chemical, Ltd. andSolvay. Though the use of PCL is certainly within the scope of theinvention, it is currently a less preferred soft biopolymer thanaliphatic-aromatic polyesters, which give overall better performance forwraps and laminate coatings.

∈-Caprolactone is a seven member ring compound that is characterized byits reactivity. Cleavage usually takes place at the carbonyl group.∈-Caprolactone is typically made from cyclohexanone by a peroxidationprocess. PCL is a polyester made by polymerizing ∈-caprolactone. Highermolecular weight PCL may be prepared under the influence of a widevariety of catalysts, such as aluminum alkyls, organometalliccompositions, such as Group Ia, IIa, IIb, or IlIa metal alkyls, Grignardreagents, Group II metal dialkyls, calcium or other metal amides oralkyl amides, reaction products of alkaline earth hexamoniates, alkalineoxides and acetonitrile, aluminum trialkoxides, alkaline earth aluminumor boron hydrides, alkaline metal or alkaline earth hydrides or alkalinemetals alone. PCL is typically prepared by initiation with an aliphaticdiol (HO—R—OH), which forms a terminal end group.

Another “soft” aliphatic polyester that may be used in manufacturing theinventive polymer blends is polyhydroxybutyrate-hydroxyvaleratecopolymer (PHBV), which is manufactured using a microbial-inducedfermentation process. One such PHBV copolyester, manufactured by theMonsanto Company, has a glass transition temperature of about 0° C. anda melting point of about 170° C. If possible, PHBV copolyesters shouldbe formulated and/or modified so as have a glass transition temperatureless than about −5° C.

In the fermentation process used to manufacture PHBV, a single bacteriumspecies converts corn and potato feed stocks into a copolymer ofpolyhydroxybutyrate and hydroxyvalerate constituents. By manipulatingthe feed stocks, the proportions of the two polymer segments can bevaried to make different grades of material. All grades are moistureresistant while still being fully biodegradable. The world producers ofPHBV are Monsanto, with its BIOPOL product, and METABOLIX, with itsvarious grades of polyhydroxy-alkanoates (PHAs). Polyhydroxyvalerate(PHV) is also an example of a “soft” polymer.

As set forth above, polyhydroxybutyrates (PHBs) can act as either astiff or soft polymer depending on their molecular weight, whether theyhave been modified using chain extenders and/or branching agents,whether they have been copolymerized with another polymer, and dependingon the other constituents within the overall thermoplastic composition.In this sense, PHBs are unique among biopolymers and may be of specialinterest for use in making wraps, laminate coatings, packagingmaterials, and the like.

Another class of “soft” aliphatic polyesters are based on repeatingsuccinate units such as polybutylene succinate (PBS), polybutylenesuccinate adipate (PBSA), and polyethylene succinate (PES). Each ofthese succinate-based aliphatic polyesters is manufactured by Showa HighPolymer, Ltd. and sold under the trade name BIONELLE. PBS (Bionolle1001) has a glass transition temperature of −30° C. and a melting pointof 114° C. PBSA (Bionolle 3001) has a glass transition temperature of−35° C. and a melting point of 95° C. PES (Bionolle 6000) has a glasstransition temperature of −4° C. and a melting point of 102° C.

The target applications for BIONOLLE include films, sheets, filaments,foam-molded products and foam-expanded products. BIONOLLE isbiodegradable in compost, in moist soil, in water with activated sludge,and in sea water. PBSA degrades rapidly in a compost environment, so itis similar to cellulose, whereas PBS degrades less rapidly and issimilar to newspaper in terms of biodegradation.

BIONOLLE is manufactured according to a patented two-step process ofpreparing succinate aliphatic polyesters with high molecular weights anduseful physical properties. In a first step, a low molecular weighthydroxy-terminated aliphatic polyester prepolymer is made from a glycoland an aliphatic dicarboxylic acid. This polymerization is catalyzed bya titanium catalyst such as tetraisopropyltitanate, tetraisopropoxytitanium, dibutoxydiacetoacetoxy titanium, or tetrabutyltitanate. In thesecond step, a high molecular weight polyester is made by reacting adiisocyanate, such as hexamethylene diisocyante (HMDI) with a polyesterprepolymer.

Showa manufactures PBS by first reacting 1,4-butanediol with succinicacid in a condensation reaction to form a prepolymer and then reactingthe prepolymer with HMDI as a chain extender.

PBSA copolymer is manufactured by first condensing 1,4-butanediol,succinic acid and adipic acid to form a prepolymer and then reacting theprepolymer with HMDI as a chain extender.

PES homopolymer is prepared by reacting ethylene glycol and succinicacid and using HMDI or diphenylmethane diisocyanate as a chain extender.

Succinate-based aliphatic polyesters are also manufactured by MitsuiToatsu, Nippon Shokubai, Cheil Synthetics, Eastman Chemical, and SunkyonIndustries.

Finally, although starch, such as modified starch or starch that hasbeen gelatinized with water and subsequently dried, is known to have ahigh glass transition temperature (i.e., 70-85° C.) and be verycrystalline at room temperature, certain forms of starch in which thecrystallinity has been greatly reduced or destroyed altogether can havevery low glass transition temperatures and may, in fact, constitute“soft” biodegradable polymers within the scope of the invention. Asdiscussed more fully below, native or dried gelatinized starch can beused as particulate fillers in order to increase the dead-foldproperties of sheets and films made from a particular polymer or polymerblend. Moreover, to the extent that starches become thermoplastic butretain a substantial portion of their crystallinity, such starches mayact as “stiff”, rather than “soft”, polymers. Nevertheless, there existsa range of thermoplastic starch polymers that can behave as “soft”polymers.

For example, U.S. Pat. No. 5,362,777 to Tomka is a landmark patent andwas the first attempt to manufacture what is known as thermoplasticallyprocessable starch (TPS). TPS is characterized as a thermoplastic starchpolymer formed by mixing and heating native or modified starch in thepresence of an appropriate high boiling plasticizer (such as glycerinand sorbitol) in a manner such that the starch has little or nocrystallinity, a low glass transition temperature, and very low water(less than 5%, preferably less than about 1% by weight while in a meltedstate after venting and prior to conditioning). When blended withappropriate hydrophobic polymers, such as the stiff polymers disclosedherein, e.g., polyesteramides such as BAK, TPS can have a glasstransition temperature as low as −60° C., and typically below about −20°C.

Although it is within the scope of the invention to includethermoplastic polymers based on starch that include plasticizers such asglycerine, sorbitol, propylene glycol and the like, it is preferable,when manufacturing wraps for use in covering food products, to utilizethermoplastic starch polymers that are made without the use of suchplasticizers, which can potentially diffuse into food. Preferredthermoplastic starch polymers for use in making food wraps mayadvantageously utilize the natural water content of native starchgranules to initially break down the granular structure and melt thenative starch. Thereafter, the melted starch can be blended with one ormore synthetic biopolymers, and the mixture dried by venting, in orderto yield a final polymer blend. Where it is desired to make food wrapsor other sheets or films intended to contact food using a thermoplasticstarch polymer made with a high boiling liquid plasticizer, it will bepreferable to limit the quantity of such thermoplastic starch polymersto less than 10% by weight of the polymer mixture, exclusive of anysolid fillers.

III. Optional Components

There are a number of optional components which may be included withinthe biodegradable polymer blends of the present invention in order toimpart desired properties. These include, but are not limited to,plasticizers, lubricants, fillers, natural polymers and nonbiodegradablepolymers.

A. Plasticizers.

Plasticizers may optionally be added in order to improve processing,such as extrusion and/or film blowing, or final mechanical properties,particularly of polymer blends that are relatively stiff. A stifferpolymer blend may be dictated by other performance criteria, such ashigh temperature stability, strength, lower elongation, higherdead-fold, resistance to “blocking” during and after processing, and thelike. In such cases, a plasticizer may be necessary in order to allowthe polymer blend to satisfy certain processing and/or performancecriteria.

Suitable plasticizers within the scope of the invention, particularlywhen incorporated into a polymer blend that is intended to be used inthe manufacture of wraps and other packaging materials that will comeinto contact with food, will preferably be safe if consumed, at least insmaller quantities.

Optional plasticizers that may be used in accordance with the presentinvention include, but are not limited to, soybean oil, caster oil,TWEEN 20, TWEEN 40, TWEEN 60, TWEEN 80, TWEEN 85, sorbitan monolaurate,sorbitan monooleate, sorbitan monopalmitate, sorbitan trioleate,sorbitan monostearate, PEG, derivatives of PEG, N,N-ethylenebis-stearamide, N,N-ethylene bis-oleamide, polymeric plasticizers suchas poly(1,6-hexamethylene adipate), and other compatible low molecularweight polymers.

Examples of lubricants include salts of fatty acids, an example of whichis magnesium stearate.

B. Solid Fillers.

Fillers may optionally be added for a number of reasons, including butnot limited to, increasing the Young's modulus, dead-fold properties,rigidity, and breathability, and for decreasing the cost and tendency ofthe polymer blend to “block” or self-adhere during processing. Certainfillers, like fibers having a high aspect ratio, may increase thestrength, fracture energy and dead-fold properties of the sheets andfilms according to the invention. The fillers within the scope of theinvention will generally fall within three classes or categories: (1)inorganic particulate fillers, (2) fibers and (3) organic fillers.

1. Inorganic Particulate Fillers

The terms “particle” or “particulate filler” should be interpretedbroadly to include filler particles having any of a variety of differentshapes and aspect ratios. In general, “particles” are those solidshaving an aspect ratio (i.e., the ratio of length to thickness) of lessthan about 10:1. Solids having an aspect ratio greater than about 10:1may be better understood as “fibers”, as that term will be defined anddiscussed hereinbelow.

Virtually any known filler, whether inert or reactive, can beincorporated into the biodegradable polymer blends. In general, addingan inorganic filler will tend to greatly reduce the cost of theresulting polymer blend. If a relatively small amount of inorganicfiller is used, the effects on the properties of the final compositionare minimized, while adding a relatively large amount of inorganicfiller will increase those effects. In those cases where adding theinorganic filler will tend to detract from a critical physicalparameter, such as tensile strength or flexibility, only so much of thefiller should be added in order to reduce the cost of the resultingcomposition, while retaining adequate mechanical properties required bythe intended use. However, in those cases where adding the inorganicfiller will improve one or more desired physical properties of a givenapplication, such as stiffness, compressive strength, dead-fold, and/orbreathability, it may be desirable to increase the quantity of addedfiller in order to provide this desired property while also provinggreatly decreased cost.

It will be appreciated that one of ordinary skill in the art, using amicrostructural engineering approach, can select the types and amount ofthe various inorganic fillers that may be included within the polymerblend in order to engineer a final material having the desiredproperties while taking advantage of the cost-reducing properties ofadding the inorganic filler.

In general, in order to maximize the quantity of inorganic filler whileminimizing the deleterious mechanical effects of adding the filler asmuch as possible, it may be advantageous to select filler particles in amanner that decreases the specific surface area of the particles. Thespecific surface area is defined as the ratio of the total particlesurface area versus the total particle volume. One way to decrease thespecific surface area is to select particles that have a more uniformsurface geometry. The more jagged and irregular the particle surfacegeometry, the greater will be the ratio of surface area to volume ofthat particle. Another way to decrease the specific surface area is toincrease the particle size. In view of the advantages of decreasing thespecific surface area of the inorganic filler, it will be preferable toinclude inorganic filler particles having a specific surface area in arange from about 0.1 m²/g to about 400 m²/g, more preferably in rangefrom about 0.15 m²/g to about 50 m²/g, and most preferably in a rangefrom about 0.2 m²/g to about 2 m²/g.

Related to decreased specific surface area in improving the rheology andfinal strength properties of the polymer blends of the present inventionis the concept of particle packing. Particle packing techniques allowfor a reduction in “wasted” interstitial space between particles whilemaintaining adequate particle lubrication and, hence, mixture rheology,within the melted polymer blend, while also allowing for more efficientuse of the thermoplastic phase as a binder in the final hardened polymerblends of the present invention. Simply stated, particle packing is theprocess of selecting one or more ranges of particle sizes in order thatthe spaces between a group of larger particles are substantiallyoccupied by a selected group of smaller particles.

In order to optimize the packing density of the inorganic fillerparticles, differently sized particles having sizes ranging from assmall as about 0.01 micron to as large as about 2 mm may be used. Ofcourse, the thickness and other physical parameters of the desiredarticle to be manufactured from any given polymer blend may oftendictate the upper particle size limit. In general, the particle packingwill be increased whenever any given set of particles is mixed withanother set of particles having an average particle size (i.e., widthand/or length) that is at least about 2 times bigger or smaller than theaverage particle size of the first group of particles. The particlepacking density for a two-particle system will be maximized whenever thesize ratio of a given set of particles is from about 3 -10 times thesize of another set of particles. Similarly, three or more differentsets of particles may be used to further increase the particle packingdensity.

The degree of packing density that will be “optimal” will depend on anumber of factors including, but not limited to, the types andconcentrations of the various components within both the thermoplasticphase and the solid filler phase, the shaping method that will beemployed, and the desired mechanical and other performance properties ofthe final articles to be manufactured from a given polymer blend. One ofordinary skill in the art will be able to determine the optimal level ofparticle packing that will optimize the packing density through routinetesting. A more detailed discussion of particle packing techniques canbe found in U.S. Pat. No. 5,527,387 to Andersen et al. For purposes ofdisclosing particle packing techniques that may be useful in maximizingor optimizing particle packing density, the foregoing patent isincorporated herein by reference.

In those cases where it is desired to take advantage of the improvedproperties of rheology and binding efficiency utilizing particle packingtechniques, it will be preferable to include inorganic filler particleshaving a natural particle packing density in a range from about 0.55 toabout 0.95, more preferably in range from about 0.6 to about 0.9, andmost preferably in a range from about 0.7 to about 0.85.

Examples of useful inorganic fillers that may be included within thebiodegradable polymer blends include such disparate materials as sand,gravel, crushed rock, bauxite, granite, limestone, sandstone, glassbeads, aerogels, xerogels, mica, clay, alumina, silica, kaolin,microspheres, hollow glass spheres, porous ceramic spheres, gypsumdihydrate, insoluble salts, calcium carbonate, magnesium carbonate,calcium hydroxide, calcium aluminate, magnesium carbonate, titaniumdioxide, talc, ceramic materials, pozzolanic materials, salts, zirconiumcompounds, xonotlite (a crystalline calcium silicate gel), lightweightexpanded clays, perlite, vermiculite, hydrated or unhydrated hydrauliccement particles, pumice, zeolites, exfoliated rock, ores, minerals, andother geologic materials. A wide variety of other inorganic fillers maybe added to the polymer blends, including materials such as metals andmetal alloys (e.g., stainless steel, iron, and copper), balls or hollowspherical materials (such as glass, polymers, and metals), filings,pellets, flakes and powders (such as microsilica).

The particle size or range of particle sizes of the inorganic fillerswill depend on the wall thickness of the film, sheet, or other articlethat is to be manufactured from the polymer blend. In general, thelarger the wall thickness, the larger will be the acceptable particlesize. In most cases, it will be preferable to maximize the particle sizewithin the acceptable range of particle sizes for a given application inorder to reduce the cost and specific surface area of the inorganicfiller. For films that are intended to have a substantial amount offlexibility, tensile strength, bending endurance and relatively lowdead-fold and breathability (e.g., plastic bags) the particle sizediameter of the inorganic filler will preferably be less than about 20%of the wall thickness of the film. For example, for a film or sheethaving a thickness of 40 microns, it will be preferable for theinorganic filler particles to have a particle size diameter of about 8microns or less.

On the other hand, it may be desirable in some cases for at least aportion of the filler particles to have a particle size diameter that isequal to or greater than the thickness of the polymeric sheet or film.Utilizing filler particles whose diameters equal or exceed the thicknessof the polymeric sheet or film disrupts the surface of the sheet or filmand increases the surface area, which can advantageously increase thebulk-hand-feel and/or dead-fold properties of the sheet or film. In thecase where the sheets or films are mono or biaxial stretched, the use oflarger filler particles creates definitive discontinuities that yieldsheets and films having a high degree of cavitation. Cavitation resultsin sheets having a touch and feel that more closely resembles the touchand feel of paper. In addition, it greatly increases the breathabilityand water vapor transmission of the sheets and films.

The amount of particulate filler added to a polymer blend will depend ona variety of factors, including the quantity and identities of the otheradded components, as well as the specific surface area, packing density,and/or size distribution of the filler particles themselves.Accordingly, the concentration of particulate filler within the polymerblends of the present invention may be included in a broad range from aslow as 0% by volume to as high as about 90% by volume of the polymerblend. Because of the variations in density of the various inorganicfillers than can be used, it may be more correct in some instances toexpress the concentration of the inorganic filler in terms of weightpercent rather than volume percent. In view of this, the inorganicfiller components can be included within a broad range from as low as 0%by weight to as high as 95% by weight of the polymer blend, preferablyin a range from about 5% to about 90% by weight.

In those cases where it is desired for the properties of thethermoplastic phase to predominate due to the required performancecriteria of the articles being manufactured, the inorganic filler willpreferably be included in an amount in a range from about 5% to about50% by volume of polymer blend. On the other hand, where it is desiredto create highly inorganically filled systems, the inorganic filler willpreferably be included in an amount in a range from about 50% to about90% by volume.

In light of these competing objectives, the actual preferred quantity ofinorganic filler may vary widely. In general terms, however, in order toappreciably decrease the cost of the resulting polymer blend and/or toimpart increased dead-fold, the inorganic filler component willtypically be included in an amount greater than about 10% by weight ofthe overall composition, preferably in an amount greater than about 15%by weight, more preferably in an amount greater than about 20% byweight, more especially preferably greater than about 30% by weight, andmost preferably in an amount greater than about 35% by weight of theoverall composition.

2. Fibers

A wide range of fibers can optionally be used in order to improve thephysical properties of the polymer blends. Like the aforementionedfillers, fibers will typically constitute a solid phase that is separateand distinct from the thermoplastic phase. However, because of the shapeof fibers, i.e., by having an aspect ratio greater than at least about10:1, they are better able to impart strength and toughness thanparticulate fillers. As used in the specification and the appendedclaims, the terms “fibers” and “fibrous material” include both inorganicfibers and organic fibers. Fibers may be added to the moldable mixtureto increase the flexibility, ductility, bendability, cohesion,elongation ability, deflection ability, toughness, dead-fold, andfracture energy, as well as the flexural and tensile strengths of theresulting sheets and articles.

Fibers that may be incorporated into the polymer blends includenaturally occurring organic fibers, such as cellulosic fibers extractedfrom wood, plant leaves, and plant stems. In addition, inorganic fibersmade from glass, graphite, silica, ceramic, rock wool, or metalmaterials may also be used. Preferred fibers include cotton, wood fibers(both hardwood or softwood fibers, examples of which include southernhardwood and southern pine), flax, abaca, sisal, ramie, hemp, andbagasse because they readily decompose under normal conditions. Evenrecycled paper fibers can be used in many cases and are extremelyinexpensive and plentiful. The fibers may include one or more filaments,fabrics, mesh or mats, and which may be co-extruded, or otherwiseblended with or impregnated into, the polymer blends of the presentinvention.

The fibers used in making the sheets and other articles of the presentinvention preferably have a high length to width ratio (or “aspectratio”) because longer, narrower fibers can impart more strength to thepolymer blend while adding significantly less bulk and mass to thematrix than thicker fibers. The fibers will have an aspect ratio of atleast about 10:1, preferably greater than about 25:1, more preferablygreater than about 50:1, and most preferably greater than about 100:1.

The amount of fibers added to the polymer blends will vary dependingupon the desired properties of the final molded article, with tensilestrength, toughness, flexibility, and cost being the principle criteriafor determining the amount of fiber to be added in any mix design.Accordingly, the concentration of fibers within the polymer blends ofthe present invention can be included in a broad range from 0% to about90% by weight of the polymer blend. If included at all, fibers willpreferably be included in an amount in a range from about 1% to about80% by weight of the polymer blend, more preferably in a range fromabout 3% to about 50% by weight, and most preferably in a range fromabout 5% to about 30% by weight of the polymer blend.

3. Organic Fillers

The polymer blends of the present invention may also include a widerange of organic fillers. Depending on the melting points of the polymerblend and organic filler being added, the organic filler may remain as adiscrete particle and constitute a solid phase separate from thethermoplastic phase, or it may partially or wholly melt and becomepartially or wholly associated with the thermoplastic phase.

Organic fillers may comprise a wide variety of natural occurring organicfillers such as, for example, seagel, cork, seeds, gelatins, wood flour,saw dust, milled polymeric materials, agar-based materials, nativestarch granules, pregelatinized and dried starch, expandable particles,and the like. Organic fillers may also include one or more syntheticpolymers of which there is virtually endless variety. Because of thediverse nature of organic fillers, there will not generally be apreferred concentration range for the optional organic filler component.

Organic fillers can partially or wholly take the place of inorganicfillers. In some cases, organic fillers can be selected that will impartthe same properties as inorganic fillers, such as to increase dead-fold,the bulk hand feel, breathability and water vapor transmission. Whenincluded at all, the organic filler component will typically be includedin an amount greater than about 5% by weight of the overall composition,preferably in an amount greater than about 10% by weight, morepreferably in an amount greater than about 20% by weight, and mostpreferably greater than about 30% by weight of the overall composition.

C. Natural Polymers.

In addition to thermoplastic starch or starch particles, other naturalpolymers that may be used within the polymer blends of the presentinvention comprise or are derivatives of cellulose, otherpolysaccharides, polysaccharide gums and proteins.

Examples of starches and starch derivatives include, but are not limitedto, modified starches, cationic and anionic starches, and starch esterssuch as starch acetate, starch hydroxyethyl ether, alkyl starches,dextrins, amine starches, phosphates starches, and dialdehyde starches.

Examples of derivatives of cellulose include, but are not limited to,cellulosic esters (e.g., cellulose formate, cellulose acetate, cellulosediacetate, cellulose propionate, cellulose butyrate, cellulose valerate,mixed esters, and mixtures thereof) and cellulosic ethers (e.g.,methylhydroxyethylcellulose, hydroxymethylethylcellulose,carboxymethylcellulose, methylcellulose, ethylcellulose,hydroxyethylcellulose, hydroxyethylpropylcellulose, and mixturesthereof).

Other polysaccharide-based polymers that can be incorporated into thepolymer blends of the invention include alginic acid, alginates,phycocolloids, agar, gum arabic, guar gum, acacia gum, carrageenan gum,furcellaran gum, ghatti gum, psyllium gum, quince gum, tamarind gum,locust bean gum, gum karaya, xanthan gum, and gum tragacanth, andmixtures or derivatives thereof.

Suitable protein-based polymers include, for example, Zein® (a prolaminederived from corn), collagen (extracted from animal connective tissueand bones) and derivatives thereof such as gelatin and glue, casein (theprinciple protein in cow milk), sunflower protein, egg protein, soybeanprotein, vegetable gelatins, gluten and mixtures or derivatives thereof.

D. Non Biodegradable Polymers.

Although polymer blends according to the invention preferably includebiodegradable polymers, it is certainly within the scope of theinvention to include one or more polymers which are not biodegradable.If the nonbiodegradable polymer generally comprises a disperse phaserather than the dominant continuous phase, polymer blends including anonbiodegradable polymer will nevertheless be biodegradable, at least inpart. When degraded, the polymer blend may leave behind anonbiodegradable residue that nevertheless is superior to the waste leftbehind by sheets and films that are entirely made of nonbiodegradablepolymers.

Examples of common nonbiodegradable polymers suitable for forming sheetsand films include, but are not limited to, polyethylene, polypropylene,polybutylene, PET, PETG, PETE, polyvinyl chloride, PVDC, polystyrene,polyamides, nylon, polycarbonates, polysulfides, polysulfones,copolymers including one or more of the foregoing, and the like.

IV. Polymer Blends

A. Concentration Ranges of Biopolymers.

The concentrations of the various components within the polymer blendwill depend on a number of factors, including the desired physical andmechanical properties of the final blend, the performance criteria ofarticles to be manufactured from a particular blend, the processingequipment used to manufacture and convert the blend into the desiredarticle of manufacture, and the particular components within the blend.One of ordinary skill in the art will be able, in light of the specificexamples and other teachings disclosed herein, to select and optimizethe concentrations of the various components through routine testing.

In view of the wide variety of polymer blends within the scope of theinvention, as well as the wide variety of different properties that maybe engineered within the blends, the hard and soft polymers may beincluded within widely varying concentration ranges. The one or morestiff polymers within the inventive blends will preferably have aconcentration in a range from about 20% to about 99% by weight of thebiodegradable polymer blend, more preferably in a range from about 55%to about 98% by weight, and most preferably in a range from about 70% toabout 95% by weight of the polymer blend.

Similarly, the soft polymers will preferably have a concentration in arange from about 1% to about 80% by weight of the biodegradable polymerblend, more preferably in a range from about 2% to about 45% by weight,and most preferably in a range from about 5% to about 30% by weight ofthe polymer blend.

The foregoing ranges are measured in terms of the blend of hard and softpolymers exclusive of any optional components that may be added, asdescribed and identified above. In the case where only a singlebiopolymer is used the foregoing ranges to do not apply.

B. Properties of the Polymer Blends.

The polymer blends may be engineered to have any desired property. Theproperties of the final article of manufacture will depend on a numberof factors, including mix design, processing conditions, post-formationprocessing, product size, particularly thickness, and the like. In thecase of sheets or films intended to be used as “wraps”, such as wrapsused to enclose meats, other perishable food items, and especially fastfood items (e.g., sandwiches, burgers and dessert items), it willgenerally be desirable to provide sheets and films having good“dead-fold” properties so that once folded, wrapped or otherwisemanipulated into a desired orientation, such wraps will tend to maintaintheir orientation so as to not spontaneously unfold or unwrap, as whichoccurs with a large number of plastic sheets and films (e.g.,polyethylene).

In order to improve the dead-fold properties of sheets or films producedtherefrom, biopolymers may be selected which yield blends having arelatively high Young's modulus, preferably greater than about 100 MPa,more preferably greater than about 150 MPa, and most preferably greaterthan about 200 MPa. In general, increasing the concentration of thestiff biopolymer will tend to increase the Young's modulus. The Young'smodulus may also be increased by loading the polymer blends with one ormore fillers, such as particulate or fibrous fillers, as describedabove.

In addition to, or instead of, increasing the Young's modulus to improvedead-fold, the sheets or films according to the invention may beoptionally processed to increase the “bulk hand feel” of a sheet, whichis done by disrupting the generally planar nature of the sheet or film.This can be done, for example, by embossing, crimping, quilting orotherwise texturing the sheet so as to have regularly spaced-apart orrandom hills and valleys rather than simply a smooth, planar sheet. Thismay be done, for example, by passing the sheet or film through a pair ofknurled or other embossing-type rollers. Such texturing increases theability of a sheet to take and maintain a fold, crinkle, creases orother bend, thus improving the dead-fold properties of the sheet.

Another way to increase the surface area of the sheets or filmsaccording to the invention so as to increase their bulk hand feel and/ordead-fold is to include particulate fillers in which at least a portionof the particles have a particle size diameter that equals or exceedsthe thickness of the polymer film or sheet. In this way, sheets andfilms can be manufactured that have dead-fold approaching or equaling100%, which exceeds the dead-fold properties of virtually allconventional paper or plastic wraps and sheets currently on the market.A rare example of a conventional sheet or wrap having 100% dead-fold isaluminum or other metal foils.

The use of fillers coupled with specific processing techniques can beused to create “cavitation”. Cavitation occurs as the thermoplasticpolymer fraction is pulled in either a monoaxial or biaxial directionand the filler particles create a discontinuity in the film or sheetthat increases in size during stretching. During stretching, a portionof the stretched polymer pulls away from the filler particles, resultingin tiny cavities in the vicinity of the filler particles. This, in turn,results in greatly increased breathability and vapor transmission of thesheets and films. It also results in films or sheets having a touch andfeel that much more closely resembles the touch and feel of paper, ascontrasted with conventional plastic sheets and films. The result is asheet, film or wrap that can be used for applications that are presentlyperformed or satisfied using paper products (i.e., wraps, tissues,printed materials, etc.)

Articles of manufacture made according to the invention can have anydesired thickness. Thicknesses of sheets and films may range from0.0001″ to 0.1″ (about 2.5 microns to about 2.5 mm). Sheets and filmssuitable for wrapping, enclosing or otherwise covering food items orother solid substrates will typically have a measured thickness betweenabout 0.0003″ and about 0.01″ (about 7.5-250 microns), and a calculatedthickness between about 0.00015″ and about 0.005″ (about 4-125 microns).The measured thickness will typically be between 10-100% larger than thecalculated thickness when the sheets and films are made fromcompositions that have a relatively high concentration of particulatefiller particles, which can protrude from the surface of the sheet orfilm. This phenomenon is especially pronounced when significantquantities of filler particles having a particle size diameter that islarger than the thickness of the polymer matrix are used.

In view of the foregoing, sheets and films suitable for use as wrapswill preferably have a measured thickness in a range from about 0.0004″to about 0.005″ (about 10 to about 125 microns), more preferably in arange from about 0.0005″ to about 0.003″ (about 12 to about 75 microns),and most preferably in a range from about 0.001″ to about 0.002″ (about25 to about 50 microns). On the other hand, sheets and films suitablefor use as wraps will preferably have a calculated thickness in a rangefrom about 0.0002″ to about 0.003″ (about 5 to about 75 microns), morepreferably in a range from about 0.0003″ to about 0.002″ (about 7.5 toabout 50 microns), and most preferably in a range from about 0.0005″ toabout 0.0015″ (about 12 to about 40 microns).

The difference between the calculated and measured thickness tends toincrease with increasing filler content and also with increasingparticle size. Conversely,the difference between the calculated andmeasured thickness tends to decrease with decreasing filler content andalso with decreasing particle size. Sheets and films that include nofillers, or lower quantities of fillers having a particle size diameterthat is substantially lower than the thickness of the polymer matrix,will have a measured thickness that is similar or equal to thecalculated thickness.

Another important property of the biodegradable blends according to theinvention is that when such blends are blown, extruded, cast, orotherwise formed into sheets and films, such sheets and films arereadily printable without further processing. Thus, another advantage ofutilizing the inventive polymer blends in the manufacture of wraps isthat such blends are generally able to accept and retain print much moreeasily than conventional plastics or waxed papers. Many plastics andwaxes are highly hydrophobic and must be surface oxidized in order toprovide a chemically receptive surface to which ink can adhere.Biopolymers, on the other hand, typically include oxygen-containingmoieties, such as ester or amide groups, to which inks can readilyadhere.

C. Measuring Dead-Fold

The term “dead-fold” refers to the tendency of a sheet or film tomaintain a crease, crinkle, fold or other bend. The dead-fold propertiesof sheets and films can be accurately measured using a standard testknown in the art. This test provides the ability to compare and contrastthe dead-fold properties of various sheets and films. The followingequipment is useful in performing the standard dead-fold test: (1) asemicircular protractor, divided along a 1″ diameter semicircle; (2) aweight consisting of a smooth-faced metal block that is 0.75±0.05″ by1.25±0.05″ and of such a thickness so as to weigh 50 g±0.05 g; (3) a1″×4″ template for cutting test specimens; (4) a timer or stopwatchcapable of timing to 1 second; (5) a utility knife or other cuttingtool; and (6) a humidity chamber.

The first step is preparation of an appropriately sized sample. In thecase where a film has different properties in the machine directioncompared to the cross-machine direction it may be useful to measure andaverage the dead-fold properties in both directions. The standard samplespecimen is a 1″×4″ strip of the sheet or film to be tested.

The second step is a conditioning step in order to ensure uniformity oftest conditions. The specimens are conditioned by placing them in ahumidity chamber at 23° C. and 50% relative humidity for a minimum of 24hours.

The third step is the actual dead-fold test of each conditioned teststrip. The specimen is removed from the humidity chamber and its weightrecorded. A light mark is made 1″ from one end of the test strip. Thetest strip is then placed on a flat surface and bent over at the markbut without creasing the strip. Next, the weight is placed squarely andgently over the bend with two thirds (or 0.5″) of the weight overlappingthe specimen so that a crease is formed, and with one third or (0.25″)of the weight overhanging the crease. The edges of the weight parallelto the strip should project evenly (about 0.125″) beyond each side ofthe strip. The weight is allowed to rest on the specimen for 10 seconds.Then it is removed. After exactly 30 seconds, the angle formed by thecrease is measured.

The foregoing process is repeated using the other side of the strip andusing as many additional strips as will give a statistically accuratemeasure of the dead-fold properties of a given sheet or film. Theaverage angle A is then input into the following formula to determinethe percentage dead-fold C for a given sample:C=100*(180−A)/180

If the angle A is 0° (i.e., where the crease is maintained so that nospring back is observed), the sample has 100% dead-fold(C=100*(180−0)/180=100%). At the other extreme, if the angle A is 180°(i.e., where the sample springs all the way back so that the sample isessentially flat, the sample has 0% dead-fold (C=100*(180−180)/180=0%).In the middle, a sample that springs back half way so as to form a rightangle has 50% dead-fold (C=100*(180−90)/180=50%).

When used to wrap foods, or whenever good dead-fold properties aredesired, sheets and films according to the invention can be manufacturedso as to have a dead-fold of at least about 50%. Preferably, such sheetsand films will have a dead-fold greater than about 60%, more preferablygreater than about 70%, and most preferably greater than about 80%.Sheets and films according to the invention have been developed thathave a dead-fold approaching or equal to 100%. By way of comparison,sheets and films made from polyethylene (e.g., for use in makingsandwich or garbage bags) typically have a dead-fold of 0%. Standardpaper wraps commonly used in the fast food industry typically have adead-fold between about 40-80%. Thus, sheets and films according to theinvention can be manufactured so as to have dead-fold properties thatmeet or exceed those of standard paper wraps, and which are many timesgreater than conventional plastic films and sheets, often orders ofmagnitude greater.

D. Methods of Manufacturing Polymer Blends, Sheets and Films.

It is within the scope of the invention to employ any mixing apparatusknown in the art of manufacturing thermoplastic compositions in order toform the polymer blends of the invention. Examples of suitable mixingapparatus that can be used to form the blends according to the inventioninclude a twin-shafted kneader with meshing screws having kneadingblocks sold by the Buss Company, a BRABENDER mixer, a THEYSOHN TSK 045compounder, which is a twin-shaft extruder with shafts rotating in thesame direction and which has multiple heating and processing zones, aBUSS KO Kneader having a heatable auger screw, a BAKER-PERKINS MPC/V-30double and single auger extruder, single or twin auger OMC extruders, aModel EPV 60/36D extruder, a BATTAGGION ME100 direct-current slow mixer,a HAAKE Reomex extruder, a COLLIN Blown Film Extruder, aBATTENFELD-GLOUCESTER Blown Film Extruder, and a BLACK-CLAWSON Cast FilmExtruder.

Many of the foregoing mixers are also extruders, which makes themsuitable for extruding films or sheets from the inventive blendsaccording to the invention. Alternatively, these blends can be madeusing transfer-line-injection technology where resin manufacturers caninject the various minor components of these blends into the main polycomponents during manufacture. One of ordinary skill in the art will beable to select and optimize an appropriate manufacturing apparatusaccording to the desired article to be manufactured. Once athermoplastic melt has been formed using any of the above-mentionedmixers, or any other appropriate mixing and melting apparatus known inthe thermoplastic art, virtually any molding, extrusion or shapingapparatus known in the thermoplastic molding or processing art can beused to produce finished articles of manufacture.

In a preferred embodiment for manufacturing sheets and films, the sheetsand films may be manufactured using a compounding twin screw extruder toprepare the blends, and a blown film or cast film line to make the filmsand sheets. Blown films and sheets tend to have similar, if notidentical, strength and other performance properties in the biaxialdirection due to how they are processed (i.e., they are extruded as atube and then expanded in all directions by blowing air within theconfines of the tube, causing it to expand like a balloon). Cast filmsor sheets, on the other hand, unless subjected to biaxial stretching,will be substantially stronger (e.g. will have substantially greatertensile strength) in the machine direction and will be substantiallymore tear resistant in the cross-machine direction. When extruding athermoplastic material, the polymer molecules tend to be oriented in themachine direction. Machine direction orientation is further increased ifthe extruded sheet or film is passed through a nip to decrease the sheetor film thickness in the machine direction.

The sheets and films according to the invention may comprise a singlelayer or multiple layers as desired. They may be formed by mono- andco-extrusion, casting and film blowing techniques known in the art.Because they are thermoplastic, the sheets can be post-treated by heatsealing to join two ends together to form sacks, pockets, pouches, andthe like. They can be laminated onto existing sheets or substrates. Theycan also be coated themselves.

Monoaxial or biaxial stretching of sheets and films can be used tocreate cavitation. Cavitation increase the breathability and vaportransmission of the sheets and films. It also results in films or sheetshaving a touch and feel that much more closely resembles the touch andfeel of paper compared to conventional thermoplastic sheets and films.

V. EXAMPLES OF THE PREFERRED EMBODIMENTS

The following examples are presented in order to more specifically teachcompositions and process conditions for forming the biodegradable blendsaccording to the present invention, as well as articles therefrom. Theexamples include various mix designs of the inventive biodegradablepolymer blends as well various processes for manufacturing the blendsand then forming sheets and films therefrom.

Examples 1-3

Films were manufactured from biodegradable polymer blends having thefollowing mix designs, with the concentrations being expressed in termsof weight percent of the entire polymer blend:

Example Biomax 6926 Ecoflex-F SiO₂ 1 94.84%  5% 0.16% 2 89.84% 10% 0.16%3 79.84% 20% 0.16%

The foregoing polymer blends were blended and blown into films at GeminiPlastics, located in Maywood, Calif., using DuPont supplied BIOMAX 6926(both new and old lots), a silica master batch in BIOMAX 6926 base resinsupplied by DuPont, and ECOFLEX-F resin obtained from BASF. The filmswere blown using a Gemini film blowing extruder (L/D 24/1) equipped witha 2 inch barrier mixing screw containing a Maddock shear mixing tip, anda 4 inch diameter annular die with a die gap of 0.032-0.035″.

Even though a typical quantity of silica antiblock was used (i.e.,0.16%), significant blocking of the film was observed for the film madeusing the mix design of Example 3 (i.e. 20% ECOFLEX); however, there wasno observed blocking of the 5 and 10% ECOFLEX blends of Examples 1 and2. For purposes of comparison, films of neat ECOFLEX and BIOMAX weremanufactured. The neat ECOFLEX films were manufactured using BASFECOFLEX-F resin and a 30% talc master batch in the same resin. The neatBIOMAX films (new and old) included 0.16% SiO₂, while the neat ECOFLEXfilms included 4.5% talc. The mechanical properties of theBIOMAX/ECOFLEX blend films and the control BIOMAX and neat ECOFLEX-Ffilms were measured under ambient conditions. The data generated is showgraphically in Charts 1-8 depicted in FIGS. 1-8, respectively.

Chart 1, depicted in FIG. 1, is a plot of the strain rate versus percentelongation at break for the various films tested. At 500 mm/min. strainrate, both new and old BIOMAX films displayed poor elongation. The neatECOFLEX films and all of the films made from the BIOMAX-ECOFLEX blendshad significantly better elongations than the neat BIOMAX films at allof the strain rates studied. On the other hand, the 20% ECOFLEX blend ofExample 3 exhibited equal or better elongation compared to the neatECOFLEX films at lower strain rates, even though these films includednearly 80% BIOMAX, which was shown to have very poor elongation.

Chart 2, depicted in FIG. 2, is a plot of percent elongation versuspercentage of ECOFLEX in the BIOMAX/ECOFLEX blends measured at a fixedstrain rate of 500 mm/min. As represented by Chart 2, there was a nearlylinear improvement in the percent elongation as the concentration ofECOFLEX was increased. Moreover, the 20% ECOFLEX blend of Example 3 hadan elongation as good as the neat ECOFLEX films.

Chart 3, depicted in FIG. 3, similarly plots the percent elongationversus the percentage of ECOFLEX in the BIOMAX/ECOFLEX blends measuredat a fixed strain rate of 1000 mm/min. Again, a dramatic improvement inthe elongation of the BIOMAX/ECOFLEX blend was seen as the concentrationof ECOFLEX reached 10 and 20%, respectively, although the trend was notas clear as the data in Chart 2, measured at a fixed strain rate of 500mm/min.

Chart 4, depicted in FIG. 4, is a plot of the strain rate versus breakstress of the various films. Again, neat ECOFLEX and all of theBIOMAX/ECOFLEX blends had significantly better break stress than theneat BIOMAX films at all of the strain rates studied. Moreover, theBIOMAX/ECOFLEX blends had significantly better break stress than theneat ECOFLEX films at all strain rates, thus showing that theBIOMAX/ECOFLEX blends are all stronger in tensile strength than eitherof neat BIOMAX or ECOFLEX.

Chart 5, depicted in FIG. 5, is a plot of the break stress versuspercent ECOFLEX in the BIOMAX/ECOFLEX blends of Examples 1-3 measured ata fixed strain rate of 500 mm/min. Once again, a nearly linear increasein break stress was observed as the concentration of ECOFLEX wasincreased. Moreover, the 20% blend of Example 3 exhibited the surprisingand unexpected result of having nearly twice the break stress as theneat ECOFLEX film, and nearly three times the break stress as the neatBIOMAX film.

Chart 6, depicted in FIG. 6, is a plot of the break stress versuspercent ECOFLEX in the BIOMAX/ECOFLEX blends of Examples 1-3 measured ata fixed strain rate of 1000 mm/min. At this strain rate, the 10% ECOFLEXblend of Example 2 had the highest break stress, with a maximum peakstress of 72 MPa.

Charts 7 and 8, depicted in FIGS. 7 and 8, respectively, plot the watervapor permeability coefficient (WVPC) of the various films as a functionof the concentration of ECOFLEX within the films. In Chart 7, theestimated trend line is based on a WVPC of 7.79×10⁻³ g·cm/m²/d/mm Hg,which is the lowest measured WVPC for a neat ECOFLEX film. In Chart 8,the estimated trend line is alternatively based on a WVPC of 42×10⁻³g·cm/m²/d/mm Hg, which is the highest measured WVPC for a neat ECOFLEXfilm. The data in Charts 7 and 8 indicate that the water vapor barrierproperties of the 5 and 10% ECOFLEX blends of Examples 1 and 2 wereessentially the same as that of the neat BIOMAX film. The WVPC data forall samples were measured by the standard procedures described in theTest Method ASTM F 1249-90.

Chart 9, depicted in FIG. 9, is a plot of the modulus of various filmsas a function of the concentration of ECOFLEX within the films.Surprisingly, the modulus of blends containing BIOMAX and ECOFLEX aresignificantly higher than of neat BIOMAX and ECOFLEX. Because one of theuses of the films manufactured according to the present invention is asa wrap having good dead-fold properties, and because the degree ofdead-fold is believed to be related to the modulus of a film, blends ofBIOMAX and ECOFLEX appear to have superior dead-fold properties overeach of the neat BIOMAX and ECOFLEX films, with the 5% and 10% blendsexhibiting the highest modulus.

Examples 4-5

Films were manufactured from biodegradable polymer blends having thefollowing mix designs, with the concentrations being expressed in termsof weight percent of the entire polymer blends:

Example Biomax 6926 Ecoflex-F Talc 4 79.7% 16.7% 3.6% 5 76.7% 16.7% 6.6%

The films were blown using a Gemini film blowing extruder (L/D 24/1)equipped with a 2 inch barrier mixing screw containing a Maddock shearmixing tip, and a 4 inch diameter annular die with a die gap of0.032-0.035″. The film of Example 5 had better dead-fold properties thanthe film of Example 4, which might be attributable to the higherconcentration of talc within the blend used in Example 5.

Example 6

A film was manufactured from a biodegradable polymer blend having thefollowing mix design, with the concentration being expressed in terms ofweight percent of the entire polymer blend:

ECOFLEX-F 20% Thermoplastic Starch 50% Polylactic Acid 15% InorganicFiller 15%

The Thermoplastic Starch was obtained from Biotec BiologischeNatuverpackungen GmbH & Co., KG (“Biotec”), located in Emmerich,Germany. The polylactic acid was obtained from Cargill-Dow Polymers,LLC, located in Midland, Mich., USA. The inorganic filler was calciumcarbonate obtained from OMYA, division Pluess-Staufer AG, located inOftringen, Switzerland.

The foregoing blend was manufactured and blown into sheets using aproprietary extrusion line thermoplastic starch extrusion/film blowingapparatus manufactured and assembled specifically for Biotec. Inparticular, the extrusion/film blowing apparatus was manufactured by Dr.Collin GmbH, located in Ebersberg, Germany. A detailed description of anextrusion/film blowing apparatus similar to the one used by Biotec isset forth in U.S. Pat. No. 5,525,281 to Lörcks et al. U.S. Pat. No.6,136,097 to Lörcks et al. discloses processes for manufacturingintermediate thermoplastic starch-containing granulates that can befurther processed to make films and sheets. For purposes of disclosure,the foregoing patents are incorporated herein by reference.

The film had a modulus of 215.65 MPa. Thus, it had excellent dead-foldproperties as a result of the inclusion of the inorganic filler and thepolylactic acid, which is a generally stiff, crystalline polymer at roomtemperature. As set forth above, PLA has a glass transition temperaturebetween 50-60° C. The ECOFLEX and thermoplastic starch (TPS) both actedas soft, low glass transition temperature polymers. The TPS, whenblended with additional polymers and at very low water, has a glasstransition temperature approaching −60° C. The ECOFLEX and TPS thusassisted the blowability and flexibility of the blend. The TPS alsoincreased the natural polymer content, thus making the film morebiodegradable.

Example 7

A film was manufactured from a biodegradable polymer blend having thefollowing mix design, with the concentration being expressed in terms ofweight percent of the entire polymer blend:

Thermoplastic Starch 30% BAK 1095 60% Inorganic Filler 10%

The thermoplastic starch was obtained from Biotec. The BAK 1095 wasobtained from Bayer AG, located in Köln, Germany, and was analiphatic-aromatic polyesteramide. The inorganic filler was calciumcarbonate obtained from OMYA, division Pluess-Staufer AG, located inOftringen, Switzerland.

The foregoing blend was manufactured and blown into sheets using theproprietary thermoplastic starch extrusion/film blowing apparatusdescribed in Example 6. The film had excellent dead-fold properties as aresult of the inclusion of the inorganic filler and the BAK 1095, whichis a somewhat stiff, crystalline polymer at room temperature even thoughit is classified as “film grade”. As set forth above, BAK 1095 behavesas if it has a glass transition temperature of at least 10° C. Becausethe glass transition temperature of BAK 1095 is relatively low comparedto PLA, considerably more BAK could be included without destroying thefilm-blowing properties and flexibility of the resulting film. The TPSacted as the soft, low glass transition temperature polymer, and furtherassisted the blowability and flexibility of the blend. It also increasedthe natural polymer content, thus making the film more biodegradable.

Examples 8-12

Films were manufactured from biodegradable polymer blends having thefollowing mix designs, with the concentrations being expressed in termof weight percent of the entire polymer blend:

Example Biomax 6926 Ecoflex F Talc TiO₂ CaCO₃ 8   76%   15% 4.5% 4.5% —9 85.5%  9.5% —   5% — 10   70% 17.5% — 2.5% 10% 11   66% 16.5% — 2.5%15% 12   58%   24% —   3% 15%

The talc was supplied by Luzenac, located in Englewood, Colo., having aparticle size of 3.8 microns. The titanium dioxide was supplied byKerr-McGee Chemical, LLC, located in Oklahoma City, Okla., grade TRONOX470, having a particle size of 0.17 micron. The calcium carbonate wassupplied by Omnia, located in Lucerne Valley, Calif., particle size of 2microns. The foregoing blends were manufactured on a Werner PfeidererZSK twin-screw extruder, and blown into sheets using a Gemini filmblowing extruder (24/1) equipped with a 2 inch barrier mixing screwcontaining a Maddock shear mixing tip, and a 4 inch diameter die. All ofthe films had excellent dead-fold properties. The polymer blends ofExamples 10-12 were also extruded into sheets using a single screwextruder and a 14 inch flat cast-film die, and the usual nip-rolls andfilm take-up assembly normal to such a system. All of these films alsohad excellent dead-fold properties.

Examples 13-61

Blown and cast films and sheets were manufactured from biodegradablepolymer blends having the following mix designs, with the concentrationsbeing expressed in term of weight percent of the entire polymer blend:

Ecoflex Eastar Bio Eastar Bio Example PLA Biomax BX 7000 Ultra GP CaCO₃TiO₂ Starch 13   30%  0% 45%   0%  8.25%  14.5% 2.25%   0% 14   30%  0%30%   0%  13.2%  23.2%  3.6%   0% 15   30%  0% 25%   0% 11.55%  20.3%3.15%   10% 16   50%  0% 25%   0%  8.25%  14.5% 2.25%   0% 17   50%  0%10%   0%  13.2%  23.2%  3.6%   0% 18   50%  0%  5%   0% 11.55%  20.3%3.15%   10% 19   50%  0%  0%   0%  16.5%  29.0%  4.5%   0% 20   50%  0% 0%   0%  13.2%  23.2%  3.6%   10% 21   50%  0%  0%   0% 11.55%  20.3% 3.2%   15% 22   50%  0%  0%   0%  9.9%  17.4%  2.7%   20% 23   50%  0% 0%   0%  8.25%  14.5% 2.25%   25% 24   27%  0% 64%   0%  2.97%  5.22%0.81%   0% 25   25%  0% 58%   0%  5.61%  9.86% 1.53%   0% 26   23%  0%54%   0%  7.59% 13.34% 2.07%   0% 27   30%  0% 40%   0%    0%  0.0% 0.0%   30% 28   15%  0% 60%   0%    0%  0.0%  0.0%   25% 29   25%  0%25%   0%  16.5%  29.0%  4.5%   0% 30   20%  0% 20%   0%  19.8%  34.8% 5.4%   0% 31   35%  0%  5%   0%  19.8%  34.8%  5.4%   0% 32   40%  0%10%   0%  16.5%  29.0%  4.5%   0% 33   50%  0%  0%   0%  16.5%  29.0% 4.5%   0% 34   20%  0%  0%  20%  19.8%  34.8%  5.4%   0% 35   27%  0%36%   0%  3.3%  5.8%  0.9%   27% 36   21%  0% 28%   0%  9.9%  17.4% 2.7%   21% 37 28.5%  0% 38%   5%    0%    0%   0% 28.5% 38   40%  0% 0%   7%  16.5%  29.0%  4.5%   3% 39   40%  0%  7%   0%  16.5%  29.0% 4.5%   3% 40   50%  0%  0%   0%  16.5%  29.0%  4.5%   0% 41   20%  0% 0%  20%  19.8%  34.8%  5.4%   0% 42   30%  0%  0%  14%  16.5%  29.0% 4.5%   6% 43   40%  0%  0%  14%  13.2%  23.2%  3.6%   6% 44   0% 40% 0%  14%  13.2%  23.2%  3.6%   6% 45   0% 50%  0%   0%  16.5%  29.0% 4.5%   0% 46   0% 45%  0%   0% 18.15%  31.9% 4.95%   0% 47   0% 40%  0%  0%  19.8%  34.8%  5.4%   0% 48   0% 40%  0%   0%  19.8%  34.8%  5.4%  0% 49   40%  0% 14%   0%  13.2%  23.2%  3.6%   6% 50   0% 30%  0%   7% 19.8%  34.8%  5.4%   3% 51   0% 35%  0%   7% 18.15%  31.9% 4.95%   3%52   0% 38%  0% 1.4%  19.8%  34.8%  5.4%  0.6% 53   0% 35%  0% 3.5% 19.8%  34.8%  5.4%  1.5% 54   40%  0%  0%  14%  13.2%  23.2%  3.6%   6%55   40%  0%  0%   0%  26.7%  22.7%  3.5%  7.1% 56   40%  0%  0% 13.8% 12.9%  22.7%  3.5%  7.1% 57   40%  0%  0% 26.7%    0%  22.7%  3.5% 7.1% 58   40%  0%  0% 13.8%  12.9%  22.7%  3.5%  7.1% 59   40%  0%  0%  0%  26.7%  22.7%  3.5%  7.1% 60   40%  0%  0%   14%  13.2%  23.2% 3.6%   6% 61   0% 50%  0%   0%  16.5%  29.0%  4.5%   0%

The compositions of Examples 13-59 were all processed and blown intofilms using a COLLIN Blown Film Extruder. The films made using thecompositions of Examples 30-34, 36, 38, 41 and 43 were tested and foundto have dead-folds of 100%, 92%, 92%, 91%, 100%, 100%, 100%, 100% and100%, respectively. Although films made from the other compositions werenot tested for dead-fold, they would be expected to have relatively highdead-fold compared to conventional biopolymers (i.e., at least about80%). The water vapor transmission rate for films made using thecompositions of Examples 36, 38, 41 and 43 were 91.94, 91.32, 98.29 and80.31 g/m²/day, respectively.

The composition of Example 60 was processed and blown into a film usinga BATTENFELD-GLOUCESTER Blown Film Extruder. A film made from thiscomposition was found to have a water vapor transmission rate of 42.48g/m²/day.

The composition of Example 61 was processed and blown into various filmsusing both a BATTENFELD-GLOUCESTER Blown Film Extruder and a BLACK-CLAWSON Cast Film Extruder. The film formed using the BATTENFELD-GLOUCESTERBlown Film Extruder apparatus was tested and found to have a dead-foldof 100%. Two different thicknesses of films were formed using theBLACK-CLAWSON Cast Film Extruder, one having a thickness of 1.3 mils(0.0013″) and another having a thickness of 1.8 mils (0.0018″). Both hada distinctive machine direction orientation because they were cast,rather than blown, films. The 1.3 mil film had a dead-fold of 99%, andthe 1.8 mil film had a dead-fold of 100%.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

1. An article of manufacture that is adapted for use as a food wrap thatis both resistant to liquids and biodegradable comprising abiodegradable sheet or film having a single layer formed by extruding,blowing or casting a thermoplastic melt formed from a biodegradablethermoplastic composition that includes: (i) at least one thermoplasticbiodegradable polymer; and (ii) at least one type of filler particles,wherein the sheet or film is stretched during processing so as to resultin cavitation comprising tiny cavities in the vicinity of the fillerparticles, wherein the sheet or film is thin and flexible so as to beeasily wrapped around a food item and possesses sufficient dead-foldthat it will remain wrapped around the food item absent application ofan external force, wherein the sheet or film, prior to being used towrap a food item, includes a first exposed surface that contacts thefood item when wrapped around the food item and a second exposed surfaceon a side of the sheet or film opposite the first exposed surface.
 2. Anarticle of manufacture as defined in claim 1, wherein the fillerparticles comprise at least one of inorganic filler particles andorganic filler particles.
 3. An article of manufacture as defined inclaim 2, wherein the inorganic filler particles have a concentrationgreater than about 10% by weight of the biodegradable thermoplasticcomposition.
 4. An article of manufacture as defined in claim 2, whereinthe inorganic filler particles have a concentration greater than about20% by weight of the biodegradable thermoplastic composition.
 5. Anarticle of manufacture as defined in claim 2, wherein the inorganicfiller particles have a concentration greater than about 30% by weightof the biodegradable thermoplastic composition.
 6. An article ofmanufacture as defined in claim 1, wherein the sheet or film hasdead-fold of at least about 50%.
 7. An article of manufacture as definedin claim 1, wherein the sheet or film has dead-fold of at least about70%.
 8. An article of manufacture as defined in claim 1, wherein thesheet or film has dead-fold of at least about 80%.
 9. An article ofmanufacture as defined in claim 1, wherein the sheet or film has ameasured thickness in a range of about 0.0003″ to about 0.01″.
 10. Anarticle of manufacture as defined in claim 1, wherein the sheet or filmhas a measured thickness in a range of about 0.0005″ to about 0.003″.11. An article of manufacture as defined in claim 1, wherein the sheetor film has a measured thickness in a range of about 0.001″ to about0.002″.
 12. An article of manufacture as defined in claim 1, wherein thesheet or film has a moisture vapor transmission rate of at least about80 g/m²/day.
 13. An article of manufacture as defined in claim 1,wherein the biodegradable thermoplastic composition includes at leastone stiff thermoplastic biodegradable polymer and at least one softthermoplastic biodegradable polymer, and optionally at least one offibers or a nonbiodegradable polymer.
 14. An article of manufacture asdefined in claim 13, wherein at least a portion of the softthermoplastic biodegradable polymer comprises thermoplastic starch thatis free of plasticizers.
 15. An article of manufacture as defined inclaim 13, wherein the stiff thermoplastic biodegradable polymercomprises at least one stiff synthetic biodegradable polymer and whereinthe soft thermoplastic biodegradable polymer comprises at least one softsynthetic biodegradable polymer.
 16. An article of manufacture asdefined in claim 1, wherein at least a portion of the filler particlesprotrude from a surface of the sheet or film.
 17. An article ofmanufacture as defined in claim 16, wherein the particles that protrudefrom the surface of the sheet or film have particle size diameters thatare greater than the thickness of the sheet or film.
 18. A sheet or filmadapted for use as a food wrap that is both resistant to liquids andbiodegradable, wherein the sheet or film is formed by extruding, blowingor casting a thermoplastic melt formed from a biodegradablethermoplastic composition that comprises at least one hydrophobicthermoplastic biodegradable polymer, wherein the sheet or film istextured by a knurled or embossing-type roller so as to have dead-foldof at least about 70%, wherein the sheet or film is thin and flexible soas to be easily wrapped around a food item and possesses sufficientdead-fold that it will remain wrapped around the food item absentapplication of an external force, wherein the sheet or film, prior tobeing used to wrap a food item, includes a first exposed surface thatcontacts the food item when wrapped around the food item and a secondexposed surface on a side of the sheet or film opposite the firstexposed surface.
 19. A sheet or film as defined in claim 18, wherein thetextured sheet or film has dead-fold of at least about 80%.
 20. A sheetor film as defined in claim 18, wherein the biodegradable thermoplasticcomposition comprises at least one stiff thermoplastic biodegradablepolymer and at least one soft synthetic thermoplastic biodegradablepolymer.
 21. A sheet or film adapted for use as a food wrap that is bothresistant to liquids and biodegradable, wherein the sheet or film isformed as a single layer by extruding, blowing or casting athermoplastic melt formed from a biodegradable thermoplastic compositionthat comprises at least one thermoplastic biodegradable polymer and atleast one type of filler particles included in an amount so that thesheet or film has dead-fold of at least about 70%, wherein the sheet orfilm is water-resistant and biodegradable, wherein the sheet or film isthin and flexible so as to be easily wrapped around a food item andpossesses sufficient dead-fold that it will remain wrapped around thefood item absent application of an external force, wherein the sheet orfilm, prior to being used to wrap a food item, includes a first exposedsurface that contacts the food item when wrapped around the food itemand a second exposed surface on a side of the sheet or film opposite thefirst exposed surface.
 22. A sheet or film as defined in claim 21,wherein the sheet or film has dead-fold of at least about 80%.
 23. Asheet or film as defined in claim 21, wherein the sheet or film hasdead-fold of about 100%.
 24. A sheet or film as defined in claim 21,wherein the filler particles are included in an amount greater thanabout 10% by weight of the biodegradable thermoplastic composition. 25.A sheet or film as defined in claim 21, wherein the filler particles areincluded in an amount greater than about 20% by weight of thebiodegradable thermoplastic composition.
 26. A sheet or film as definedin claim 21, wherein the filler particles are included in an amountgreater than about 30% by weight of the biodegradable thermoplasticcomposition.
 27. A sheet or film as defined in claim 21, wherein thebiodegradable thermoplastic composition comprises at least one stiffsynthetic hydrophobic thermoplastic biodegradable polymer and at leastone soft synthetic thermoplastic biodegradable polymer.
 28. A sheet orfilm as defined in claim 21, wherein at least a portion of the fillerparticles protrude from a surface of the sheet or film.
 29. An articleof manufacture comprising a single layer biodegradable sheet or filmadapted for use as a food wrap that is both resistant to liquids andbiodegradable, wherein the sheet or film is formed by extruding, blowingor casting a biodegradable thermoplastic composition that comprises atleast one thermoplastic biodegradable polymer and at least one type offiller particles, wherein at least a portion of the filler particlesprotrude from a surface of the sheet or film, wherein the sheet or filmis thin and flexible so as to be easily wrapped around a food item andpossesses sufficient dead-fold that it will remain wrapped around thefood item absent application of an external force, wherein the sheet orfilm, prior to being used to wrap a food item, includes a first exposedsurface that contacts the food item when wrapped around the food itemand a second exposed surface on a side of the sheet or film opposite thefirst exposed surface.
 30. An article of manufacture as defined in claim29, wherein the filler particles comprise at least one type of inorganicfiller particles, and wherein the sheet or film is stretched duringprocessing so as to result in cavitation comprising tiny cavities in thevicinity of the filler particles.
 31. An article of manufacture asdefined in claim 29, wherein at least a portion of the filler particleshave particle size diameters that exceed the thickness of the sheet orfilm.
 32. An article of manufacture as defined in claim 29, wherein atleast a portion of the thermoplastic biodegradable polymer comprises atleast one stiff synthetic thermoplastic biodegradable polymer and atleast one soft synthetic thermoplastic biodegradable polymer.
 33. Anarticle of manufacture comprising a single layer film or sheet formed byextrusion, blowing or casting a thermoplastic melt formed from abiodegradable thermoplastic composition comprising: at least one stiffthermoplastic biodegradable polymer having a glass transitiontemperature greater than about 10° C.; and at least one softthermoplastic biodegradable polymer having a glass transitiontemperature less than about 0° C., at least a portion of the softthermoplastic biodegradable polymer comprising an aliphatic-aromaticcopolyester, the biodegradable thermoplastic composition includingstarch that is free of plasticizers and that retains a substantialportion of its crystallinity in order for the starch to (i) act as afiller within the film or sheet and/or (ii) act as a stiff thermoplasticpolymer within the film or sheet and/or (iii) impart dead-fold to thefilm or sheet.
 34. An article of manufacture as defined in claim 33,wherein the film or sheet has dead-fold of at least about 70%.
 35. Anarticle of manufacture as defined in claim 33, wherein the film or sheethas dead-fold of at least about 80%.